Using the Serial Peripheral Interface to Communicate

Transcript

Freescale Semiconductor
Application Note
AN991/D
Rev. 1, 1/2002
Freescale Semiconductor, Inc...
Using the Serial Peripheral
Interface to Communicate
Between Multiple
Microcomputers
General Description
As the complexity of user applications increases, many designers find
themselves needing multiple microprocessors to provide necessary
functionality in a circuit. Communication between multiple processors can often
be difficult, especially when differing processors are used. A possible solution
to this problem is usage of the serial peripheral interface (SPI), an interface
intended for communication between integrated circuits on the same printed
wire board. The MC68HC05C4 is one of the first single-chip microcomputers to
incorporate SPI into hardware. One advantage of the SPI is that it can be
provided in software, allowing communication between two microcomputers
where one has SPI hardware and one does not. Special interfacing is
necessary when using the hardware SPI to communicate with a microcomputer
that does not include SPI hardware. This interface can be illustrated with a
circuit used to display either temperature or time, that incorporates both a
MC68HC05C4 and a MC68705R3. The MC68HC05C4 monitors inputs from a
keypad and controls the SPI data exchange, while the MC68705R3 determines
temperature by performing an analog-to-digital conversion on inputs from a
temperature sensor and controls the LED display. Communication between the
microcomputers is handled via SPI, with the MC68HC05C4 handling
exchanges in hardware, and the MC68705R3 handling them in software.
Usage of software SPI can be expanded to include circuits where the singlechip implementing the SPI in software controls the data exchange, and those
in which neither single-chip has hardware SPI capability. Minor modifications to
the SPI code are necessary when data exchanges are controlled by software.
Debugging designs including multiple processors can often be confusing.
Some of the confusion can be alleviated by careful planning of both the physical
debugging environment and the order in which software is checked.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
© Motorola, Inc., 1994, 2002
For More Information On This Product,
Go to: www.freescale.com
Freescale Semiconductor, Inc.
AN991/D
Serial Peripheral Interface
Communication between the two processors is handled via the serial
peripheral interface (SPI). Every SPI system consists of one master and one or
more slaves, where a master is defined as the microcomputer that provides the
SPI clock, and a slave is any integrated circuit that receives the SPI clock from
the master. It is possible to have a system where more than one IC can be
master, but there can only be one master at any given time. In this design, the
MC68HC05C4 is the master and the MC68705R3 is the slave. Four basic
signals, master-out/slave-in (MOSI), master-in/slave-out (MISO), serial clock
(SCK), and slave select (SS), are needed for an SPI. These four signals are
provided on the MC68HC05C4 on port D, pins 2–5.
Signals
The MOSI pin is configured as a data output on the master and a data input on
the slave. This pin is used to transfer data serially from the master to a slave,
in this case the MC68HC05C4 to the MC68705R3. Data is transferred most
significant bit first.
Data transfer from slave to master is carried out across the MISO,
master-in/slave-out, line. The MISO pin is configured as an input on the master
device and an output on the slave device. As with data transfers across the
MOSI line, data is transmitted most significant bit first.
All data transfers are synchronized by the serial clock. One bit of data is
transferred every clock pulse, and one byte can be exchanged in eight clock
cycles. Since the serial clock is generated by the master, it is an input on the
slave. The serial clock is derived from the master’s internal processor clock,
and clock rate is selected by setting bits 0 and 1 of the serial peripheral control
register to choose one of the four divide-by values. Values for the MCUs crystal
oscillators and the SPI divide-by must be chosen so that the SPI clock is no
faster than the internal processor clock on the slave.
The last of the four SPI signals is the slave select (SS). Slave select is an active
low signal, and the SS pin is a fixed input which is used to enable a slave to
receive data. A master will become a slave when it detects a low level on its SS
line. In this design, the MC68HC05C4 is always the master, so its SS line is tied
to VDD through a pull-up resistor.
2
Between Multiple Microcomputers
AN991/D
Serial Peripheral Interface
Registers
Three registers unique to the serial peripheral interface provide control, status,
and data storage.
The Serial Peripheral Control Register (SPCR), shown in Figure 1, provides
control for the SPI.
Address: $000A
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
SPIE
SPE
—
MSTR
CPOL
CPHA
SPR1
SPR0
0
0
0
0
0
1
U
U
U = Unaffected
Figure 1. Serial Peripheral Control Register (SPCR)
SPIE — Serial Peripheral Interrupt Enable
0 = SPIF interrupts disabled
1 = SPI interrupt if SPIF = 1
SPE — Serial Peripheral System Enable
0 = SPI system off
1 = SPI system on
MSTR — Master Mode Select
0 = Slave mode
1 = Master mode
CPOL — Clock Polarity
When the clock polarity bit is cleared and data is not being transferred, a
steady state low value is produced at the SCK pin on the master device.
Conversely, if this bit is set, the SCK pin will idle high. This bit is also used
in conjunction with the clock phase control bit to produce the desired clockdata relationship between master and salve. See Figure 2.
CPHA — Clock Phase
The clock phase bit, in conjunction with the CPOL bit, controls the clock-data
relationship between master and slave. The CPOL bit can be thought of as
simply inserting an inverter in series with the SCK line. The CPHA bit selects
one of two fundamentally different clocking protocols. When CPHA = 0, the
shift clock is the OR of SCK with SS. As soon as SS goes low the transaction
begins and the first edge of SCK involves the first data sample. When
CPHA = 1, the SS pin may be thought of as a simple output enable control.
Refer to Figure 2.
3
AN991/D
SS
SCK
(CPOL = 0, CPHA = 0)
SCK
SCK
SCK
MISO/MOSI
MSB
6
5
4
3
2
1
LSB
INTERNAL STROBE FOR DATA CAPTURE (ALL MODES)
Figure 2. Data Clock Timing
SPR1 and SPR0 — SPI Clock Rate Selects
These two serial peripheral rate bits select one of four baud rates (Table 1)
to be used as SCK if the device is a master; however, they have no effect in
the slave mode.
Table 1. Serial Peripheral Rate Selection
SPR1
SPR0
Internal Processor
Clock Divide By
0
0
2
0
1
4
1
0
16
1
1
32
Data for the SPI is transmitted and received via the Serial Peripheral Data
Register (SPDR). A data transfer is initiated by the master writing to its SPDR.
If the master is sending data to a slave, it first loads the data into the SPDR and
then transfers it to the slave. When reading data, the data bits are gathered in
the SPDR and then the complete byte can be accessed by reading the SPDR.
4
AN991/D
Demonstration Board Description
Demonstration Board Description
A keypad input from the user is used to choose the output display function. The
MC68HC05C4 monitors the keypad, decodes any valid inputs, and sends the
data to the MC68705R3. If the user has requested a temperature display, the
MC68705R3 sends a binary value of temperature in degrees farenheit to the
MC68HC05C4, where the value is converted to a celcius binary coded decimal
value and returned to the MC68705R3 to be displayed. The LEDs are common
anode display and are driven directly off of port B of the MC68705R3. If the user
desires the circuit to function as a real-time clock, a starting time must be
entered and transmitted from the MC68HC05C4 to the MC68705R3. Once the
clock has been initialized, the MC68705R3 updates the clock every minute.
Clock values are stored in memory, and when the circuit is functioning as a
thermometer, the values in memory are updated as required to maintain clock
accuracy.
Using the A/D Converter to Monitor Temperature
Temperature monitoring is performed by the Freescale MTS102 silicon
temperature sensor and the LM358 Dual Low-Power Operational Amplifier, as
shown in the schematic in Figure 3. Variations in the base-emitter voltage of
the Freescale MTS102 silicon temperature sensor are monitored by the
MC68705R3, which converts these analog inputs to equivalent digital values in
degrees farenheit. The sensor voltage is buffered, inverted, and amplified by a
dual differential amplifier before entering the A/D converter. An amplifier gain
of 16 is used, resulting in 20-millivolt steps per degree farenheit. Using a VCC
of 5 volts, the maximum differential amplifier output is 3.8 volts, resulting in a
temperature sensing range of –40 degrees to +140 degrees farenheit.
The output from the differential amplifier is connected to the A/D converter on
the MC68705R3. A block diagram of the successive approximation A/D
converter is shown in Figure 4. Provision is made for four separate external
inputs and four internal analog channels.
Two different registers associated with the converter control channel selection,
initiate a conversion, and store the result of a completed conversion. Both the
external and the internal input channels are chosen by setting the lower 3 bits
of the A/D Control Register (ACR). The internal input channels are connected
to the VRH/VRL resistor chain and may be used for calibration purposes.
The converter operates continuously, requiring 30 machine cycles per
conversion. Upon completion of a conversion, the digital value of the analog
input is placed in the A/D result register (ARR) and the conversion complete
flag, bit 7 of the ACR is set. Another sample of the selected input is taken, and
a new conversion is started.
5
6
24 pF
VCC
1 µF
4.7 k
VCC
4.7 k
39
24
8
3
6
1
20
19
OSC2
OSC1
AN0
TMR
INT
XTAL
VSS
VRL
VRH
4.7 k
1 µF
40
4
5
6
7
8
9
10
11
34
33
32
31
0.01 µF
7
2
VPP RESET
15
C6
14
C5
13
C4
12
C3
11
C2
10
C1
9
C0
25
B0
26
B1
27
B2
28
B3
29
B4
30
B5
31
B6
VSS
20
VDD
PA7
PA6
PA5
PA4
PA3
PA2
PA1
PA0
SS
SCK
MOSI
MISO
VCC
VDD
4
7
10
12
8
5
9
6
R2
240 k 1%
7
11
4
R1
6
14
15k
100 k
R3
15 k 1%
VCC
1
11 2 7 8 12 13 1
G F E D C B A
VCC
50 k
10 TURN
6
–
+ 5
VCC
100
MANB1
LED
DISPLAYS
COMMON
ANODE
2N2907
10
12
7
4
15 k
5
15 k
8
14
2
–
+ 3
G F E D C B A
VCC
15k
U2
LM358
9
14
MTS102
0.001 µF
47 k
VCC
G F E D C B A
VCC
VSS
Figure 3. Serial Peripheral Interface Demonstration Schematic
4
VCC
VCC
2
IRQ
28
PC0
10 M
3.579 MHz
VCC
TO PIN 16, PC7
30 pF
1 MHz
30 pF
MC68HC05C4
14
G F E D C B A
VCC
AN991/D
AN991/D
Using the A/D Converter to Monitor Temperature
8
D/A
15 kΩ (TYP)
8
1-OF-8
SELECT
MULTIPLEXERS
ACR1
0
ACR2
7
A/D
CONTROL
REGISTER
7
ACR0
PD0/AN0
PD1/AN1
PD2/AN2
PD3/AN3
COUNT
VRH/2 VRH/4
ACR7
VRH
VRL
CONTROL
LOGIC
COMP
0
A/D
RESULT
REGISTER
Figure 4. A/D Block Diagram
Conversions are performed internally in hardware by a simple bisection
algorithm. The D/A converter (DAC) is initially set to $80, the midpoint of the
available conversion range. This value is compared with the input value and, if
the input value is larger, $80 becomes the new minimum conversion value and
the DAC is once again set to the midpoint of the conversion range, which is now
$C0. If the input value is less than $80, $80 becomes the maximum conversion
value and the DAC is set to the midpoint of the new conversion range, in this
case $40. This process is repeated until all eight bits of the conversion are
determined.
Quantizing errors are reduced to +1/2 LSB, rather than +0, –1 LSB, through
usage of a built-in 1/2 LSB offset. Ignoring errors, the transition between 00 and
01 will occur at 1/2 LSB above the voltage reference low, and the transition
between $FE and $FF will occur 1-1/2 LSBs below voltage reference high.
The A/D converter returns a value of $30 when given an input of zero degrees
farenheit, so $30 must be subtracted from the result before converting to
celcius. This offset must also be considered when calibrating the sensor.
Calibration of the temperature sensor can be performed by adjusting the
variable resistor to produce a display of $00 after a piece of ice has been placed
on the temperature sensor for approximately one minute. A 00 display results
from a value of $50 in the ARR, so the variable resistor should be adjusted until
this value is reached.
7
AN991/D
Communication Considerations
In this application, an SPI read or write is initiated via an interrupt from the MCU
desiring to write data. When any of the three function keys, display
temperature, set time, or display time, are pressed, the MC68HC05C4, as
master, sends the MC68705R3 an interrupt on the MC68705R3’s INT pin. The
MC68HC05C4 writes the key value to its serial peripheral data register, thereby
initiating the SPI. It then waits for the SPIF bit to go high and returns to scanning
the keypad.
At the same time the MC68HC05C4 is writing to its SPDR, the MC68705R3
sets a bit counter to eight and waits for the first SCK from the MC68HC05C4.
After each clock pulse, the MC68705R3 checks the status of the data bit, sets
the carry bit equal to the data bit, and rotates the carry bit left into a result
register. The bit counter is decremented, compared to zero, and if not zero, the
MC68705R3 waits for the next clock pulse and repeats the cycle.
To ensure proper data transfers, the internal processor clock of the
MC68705R3 must be sufficiently faster than the SPI clock of the MC68HC05C4
to allow the MC68705R3 time to complete this routine before the
MC68HC05C4 can send another bit. This requires the user to first write the
code to handle the software SPI, count machine cycles, and then choose MCU
oscillator values that allow the additional machine cycles required in a software
SPI to be completed before the master can send another clock pulse to the
slave.
For example, consider the following piece of code for the MC68705R3, a slave
receiving data from the master.
DATA IN
SCK
Cycles
2
5
10
10
6
6
4
-43
PORTC pin 5
PORTC pin 4
NXT
STR
LDA
STA
BRSET
BRSET
ROL
DEC
BNE
Instruction
#$08
BITCT
4,PORTC,*
5,PORTC,STR
RESULT
BITCT
NXT
Set bit counter
Wait for clock transition
Check data status
Store in result
Check for end of byte
Get next bit
Execution of this code requires 43 machine cycles. The maximum oscillator
speed for an MC68705R3 is 1 MHz, requiring an SPI clock no greater than
1/43 MHz. One way of obtaining this rate for the SPI clock is to run the
MC68HC05C4 at 0.5 MHz and choose a divide-by 32 to generate the SPI clock.
8
AN991/D
Additional Uses of SPI
If the user has selected a temperature display, it is necessary for the
MC68705R3, as a slave, to send data to the MC68HC05C4 master. When the
MC68705R3 is ready to send data, it interrupts the MC68HC05C4 via the
MC68HC05C4’s IRQ line. The MC68HC05C4 then writes to its serial peripheral
data register to initiate the transfer and shifts in data bits sent from the
MC68705R3 until the SPIF bit goes high. While the MC68HC05C4 is writing to
its SPDR, the MC68705R3 program is setting a bit counter to 8. When it detects
a clock pulse on the SCK pin, the data register is rotated left one bit, placing
the MSB in the carry. The MOSI pin is then set equal to the carry bit, the bit
counter is decremented and, if it is greater than zero, the process is repeated.
Many variations of this usage of the SPI are possible. The three possibilities
are:
•
Hardware SPI at both master and slave
•
Software SPI at the master and hardware at the slave
•
Software SPI at both master and slave
Table 1 shows the various MCUs that have SPI implemented in hardware.
SPI is fairly straightforward in a circuit where both master and slave have
hardware SPI capability. In this case, the MCUs are connected as shown in
Figure 5 and Figure 6. Figure 5 illustrates a single master system, and
Figure 6 shows a system where either MCU can be system master. When both
master and slave have SPI capability in hardware, data transfers can be
handled full duplex. For a single master system, both master and slave write
the data to be transferred to their respective serial peripheral data registers. A
data transfer is initiated when the master writes to its serial peripheral data
register. A slave device can shift data at a maximum rate equal to the CPU
clock, so clock values must be chosen that allow the slave to transfer data at a
rate equal to the master’s transfer rate. In a multiple master system, the master
must pull the slave’s SS line low prior to writing to its serial peripheral data
register and initiating the transfer.
Programming a
Master for Software
SPI
When the master in an SPI system does not have hardware SPI capabilities,
the resulting system is quite different. An SPI system with a master providing
the SPI in software is shown in Figure 7. This system only requires two lines
between the microcomputers; data and clock. A slave select line can be added
for use with multiple slaves. If operated with one data line, the SPI will function
half-duplex only. Data is stored in a register, rotated left one bit at a time, and
a port pin is set equal to the data bit. The master then provides the serial clock
by toggling a different port pin. A bit counter must also be used to count the
eight bits in the byte.
9
AN991/D
CLOCK
DATA OUT
SPI
MC68HC05C4
SPI
MASTER
SPI OUTPUT
PERIPHERAL IC
DATA IN
SLAVE SELECT 1
PORT
SLAVE SELECT 2
SPI INPUT
PERIPHERAL IC
SLAVE SELECT 3
ANOTHER MCU
SPI SLAVE
SLAVE PERIPHERAL PROCESSOR MAY BE
ANOTHER MC68HC05C4, OR PERHAPS
AN M6804 FAMILY SINGLE-CHIP MCU
Figure 5. Single Master SPI
CLOCK
DATA
DATA
SPI
MC68HC05C4
SPI
MASTER/SLAVE
SPI
SLAVE SEL
SLAVE SEL
PORT
MC68HC05C4
SPI
MASTER/SLAVE
PORT
SYNC
SPI
SLAVE SEL
OTHER PROCESSORS MAY BE
USED, SOME FORTHCOMING
M6801,M6805, AND M6804
FAMILY VERSIONS HAVE SPI FACILITIES.
Figure 6. Multiple Master SPI
10
MC68HC05C4
SPI
MASTER/SLAVE
PORT
AN991/D
CLOCK
SPI MASTER
MCU
DATA
SPI SLAVE
MCU
Figure 7. Software SPI
Bit manipulation instructions are very useful for implementing SPI in software.
One possible software implementation for a write from the master to the slave
is shown below.
DATA OUT
SCK
PORTC pin 0
PORTC pin 1
LDX #$08
LDA DATA
RPT
ROLA
BCS SET
BCLR 0,PORTC
CLK
BSET 1,PORTC
BCLR 1,PORTC
DECX
BNE RPT
SET
BSET 0,PORTC
BRA CLK
Bit counter
Put data in register A
Shift a data bit into carry
Check for a 1
Set data out line to 0
Toggle clock pin
It not, repeat
Go to clock
Full-duplex operation requires a second data line. One port pin is then devoted
to data-out and one to data-in. Data transfer from slave to master is
accomplished immediately before the SCK pin is toggled. The state of the datain pin is tested, and the carry is then set equal to the data-in pin. This value is
then rotated into a result register. The modified code is shown below.
DATA OUT
SCK
DATA IN
PORTC pin 0
PORTC pin 1
PORTC pin 2
LDX #$08
LDA DATA
BCLR 1,PORTC
RPT
ROLA
BCS SET
BCLR 0,PORTC
BSET 1,PORTC
DIN
BRCLR3,PORTC,CLK
CLK
ROL DATAIN
DECX
BNE RPT
SET
BSET 0,PORTC
BRA DIN
Bit counter
Put data in register A
Clear clock pin
Shift a data bit into carry
Check for a 1
Set clock pin
Check state of data
Rotate input data one bit
If not, repeat
Go to data input
11
AN991/D
Programming a
Slave for Software
SPI
If the slave in the system is a MCU with hardware SPI capability, the data
transfer will happen automatically, one bit per clock pulse. If the slave is a MCU
that does not have SPI implemented in hardware, a read requires the following
actions. A bit counter is set to eight, the slave polls its SCK pin waiting for a
clock transition, once it perceives a clock it checks its data-in pin, sets the carry
equal to the data and rotates the carry into a results register. One possible code
implementation is shown in the previous timing example.
Converting this to full duplex operation requires the addition of a write from
slave to master. The slave rolls a data register to place the data bit to be sent
into the carry, and the data-out pin is set equal to the carry. These actions occur
prior to the read of data from the master. With these modifications, the code
looks as shown below.
DATA OUT
DATA IN
SCK
AGN
STR
PORTC pin 6
PORTC pin 5
PORTC pin 4
LDA
#$08
STA
BITCT
BRSET
4,PORTC,*
ROL
RES1
BCS
SET1
BCLR
6,PORTC
BRCLR
4,PORTC,*
BRSET
5,PORTC,STR
ROL
RESULT
DEC
BITCT
BNE
AGN
Set bit counter
Wait for clock
Shift data to send
Check data status
If 0, clear data out
Wait for clock transition
Check input data status
Store in result
Debugging Tips
Debugging a circuit containing two microcomputers presents various problems
not evident when working with a single microcomputer circuit. The first problem
is simultaneously providing emulation for both microcomputers. Once
emulation capability is arranged, the designer needs to keep track of the
progress of each single-chip, and monitor how the actions of one affects the
actions of the other.
One of the easiest methods to debug a circuit of this type is to use two emulator
stations, complete with separate terminals. Any emulators can be used, but
user confusion is reduced if the emulators have similar commands and syntax.
Physical separation also helps reduce confusion.It is somewhat easier to keep
track of the concurrent operations if one side of the prototype board is devoted
to each single-chip and the majority of peripherals they each must interface
with, and the emulator for that microcomputer is placed to that side of the
printed circuit board.
12
AN991/D
Conclusion
Before starting simultaneous debugging, it is best to individually debug the
code for each microcomputer wherever possible. Once it becomes necessary
for the microcomputers to communicate with one another, halt one of the
microcomputers anytime they are not actually talking and work with the
remaining microcomputer. As the debugging progresses, keep in mind that an
error in the function of one single-chip does not necessarily indicate an error in
the corresponding code for that single-chip, but rather, the error may have been
caused by an incorrect or unintended transmission from the other single-chip.
Although the aforementioned suggestions reduce debugging problems, some
will remain. Long periods of debug can result in an obscuring of the separation
of the functions of the two programs. It helps to take periodic breaks to get away
from the system and clear the thought processes. Expect to occasionally be
confused, be willing to retrace sections of code multiple numbers of times, and
the debugging will proceed fairly smoothly.
Conclusion
The Serial Peripheral Interface can be used as a tool to interconnect to MCU
with various other MCUs or peripherals, and can be used with any
microcomputer. A special case occurs when one, or more, of the MCUs in a
circuit do not have SPI capability in hardware. In this case, a simple software
routine can be written to perform the SPI. Used in this manner, the SPI
eliminates the need for costly, inconvenient parallel expansion buses and
Universal ‘Asynchronous Receiver/Transmitters (UARTs) and simplifies the
design effort.
13
AN991/D
Code Listings
0001
0002
0003
0004
0005
0006
0007
0008
0009
0010
0011
0012
0013
0014
0015
0016
0017
0018
0019
0020
0021
0022
0023
0024
0025
0026
0027
0028
0029
0030
0031
0032
0033
0034
0035
0036
0037
0038
0039
0040
0041
0042
0043
0044
0045
0046
0047
0048
0049
0050
0051
0052
0053
0054
0055
14
nam spicnt
************ REGISTER ADDRESS DEFINITION ************
0000
0002
0003
0004
0006
000A
000B
000C
0012
porta
portc
portd
ddra
ddrc
spcr
spsr
spdr
tcr
00B0
00B0
00B1
00B2
00B3
00B4
00B8
00B9
rwno
tmpa
dctr
ct1
base
lsb
msb
0020
equ
equ
equ
equ
equ
equ
equ
equ
equ
0
2
3
4
6
$0a
$0b
$0c
$12
org
$b0
rmb
rmb
rmb
rmb
rmb
rmb
rmb
1
1
1
1
4
1
1
org
$20
************ KEYPAD LOOUP TABLE ************
0020
0020
0021
0022
0023
0024
0025
0026
0027
0028
0029
002A
002B
002C
002D
002E
002F
kypd
07
04
01
00
08
05
02
0A
09
06
03
0E
0D
0C
0F
0B
0100
0100
0101
0103
0105
9C
3F 12
AE 7B
BF 02
start
equ
*
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
$07
$04
$01
$00
$08
$05
$02
$0a
$09
$06
$03
$0e
$0d
$0c
$0f
$0b
org
$100
program start
rsp
clr
ldx
stx
tcr
#$7b
portc
mask timer interrupts
disp. temp.
set time
am
pm
disp. time
blank
initialize port c
AN991/D
Code Listings
0056
0057
0058
0059
0060
0061
0062
0063
0064
0065
0066
0067
0068
0069
0070
0071
0072
0073
0074
0075
0076
0077
0078
0079
0080
0081
0082
0083
0084
0085
0086
0087
0088
0089
0090
0091
0092
0093
0094
0095
0096
0097
0098
0099
0100
0101
0102
0103
0104
0105
0106
0107
0108
0109
0110
0111
0112
0113
0107
0109
010B
010D
010F
0111
0113
AE
BF
BF
3F
A6
B7
9B
7F
0A
06
00
F0
04
ldx
stx
stx
clr
lda
sta
sei
#$7f
spcr
ddrc
porta
#$f0
ddra
set spi cont. reg.
set c0 as output
clear keypad inputs
set up port a
a7-a4 out., a0-a3 in
** check keypad **
0114
0117
0119
011B
011D
011F
0121
0123
0125
0127
CD
A1
27
A1
27
A1
27
A1
27
20
01 67
0A
0E
0E
2B
0F
06
0B
02
EB
key
jsr
cmp
beq
cmp
beq
cmp
beq
cmp
beq
bra
keypad
#$0a
dtmp
#$0e
sttm
#$0f
dtmp
#$0b
dtmp
key
check for disp. temp
check for set time
check for disp. time
check for disp. sec
wait for next input
** display temp **
0129
012B
012E
0130
0132
11
CD
A1
27
20
02
01 59
0A
02
E0
dtmp
0134 9A
0135 20 DD
0137
013A
013C
013E
0140
0142
0144
0146
0148
014A
014C
014F
0151
0153
0155
0157
CD
A1
27
A1
27
A1
27
A1
27
11
CD
A1
27
A1
27
20
01 67
0A
F9
0B
F5
0E
F1
0F
ED
02
01 59
0C
C1
0D
BD
DE
bclr
jsr
cmp
beq
bra
0,portc
spiwr
#$0a
cir
key
cir
bra
cli
key
** set time **
nudig
jsr
cmp
beq
cmp
beq
cmp
beq
cmp
beq
sttm
bclr
jsr
cmp
beq
cmp
beq
bra
keypad
#$0a
nudig
#$0b
nudig
#$0e
nudig
#$0f
nudig
0,portc
spiwr
#$0c
key
#$0d
key
nudig
send interruptfor spi
send byte
check for disp. temp.
look for valid digit
send int. for
send value
check for pm
yes, wait for
check for am
yes, wait for
get next time
spi
next input
next input
digit
** spi write subroutine **
0159
0159
015B
015E
0160
spiwr
B7 0C
0F 0B FD
10 02
81
equ
sta
brclr
bset
spiflg rts
*
spdr
7,spsr,*
0,portc
put data in data reg.
wait for end of byte
done
15
AN991/D
0114
0015
0016
0017
0118
0119
0120
0121
0122
0123
0124
0125
0126
0127
0128
0129
0130
0131
0132
0133
0134
0135
0136
0137
0138
0139
0140
0141
0142
0143
0144
0145
0146
0147
0148
0149
0150
0151
0152
0153
0154
0155
0156
0157
0158
0159
0160
0161
0162
0163
0164
0165
0166
0167
0168
0169
0170
0171
0172
0173
0174
16
** spi read subroutine **
0161
0161 BF 0C
0163 0F 0B FD
0166 81
spird
rdend
equ
stx
brclr
rts
*
spdr
7,spsr,*
initiate transfer
wait for end of byte
** keypad scanning routine **
0167
keypad equ
*
** 32 msec delay **
0167
0169
016B
016D
016E
0170
0172
0174
0175
0177
0179
0178
017D
017F
0181
0183
0184
0186
0188
A6
B7
A6
4A
26
3A
26
5F
A6
B7
B6
A4
A1
26
37
5C
A3
23
20
20
B3
32
wtlp
otlp
inlp
FD
B3
F7
80
00
00
0F
00
09
00
03
F1
DD
nxtr
inval
lda
sta
lda
deca
bne
dec
bne
clrx
lda
sta
lda
and
cmp
bne
asr
incx
cpx
bls
bra
#$20
ct1
#$32
inlp
ct1
otlp
#$80
porta
porta
#$0f
#$00
debnc
porta
#$03
nxtr
wtlp
set up outer loop
counter
set up inner loop
dec. inner loop
when 0,
decrement outer loop
set up row counter
check first row
check for key
mask upper nibble
look for zero
branch if have a key
try next row
decrement row counter
check for zero
test next row
no key pressed
** debounce key input **
018A
018C
018E
0190
0191
0193
0195
0197
0199
B7
BF
A6
4A
26
B6
A4
B1
26
B1
B0
FF
debnc
loop
FD
00
0F
B1
CC
sta
stx
lda
deca
bne
lda
and
cmp
bne
tmpa
rwno
#$ff
save value
save row number
set up delay
loop
porta
#$0f
tmpa
wtlp
wait
check row again
mask upper nibble
check for same key
return if invalid
** wait for key release **
019B
019D
019F
01A1
B6
A4
A1
26
00
0F
00
F8
wtr
lda
and
cmp
bne
porta
#$0f
#$00
wtr
check value
mask upper nibble
look for zero
wait for release
** decode key value **
01A3
01A5
01A6
01A7
01A9
01AA
01AC
B6 B1
5F
44
25 03
5C
20 FA
58
nxtc
col
lda
clrx
lsra
bcs
incx
bra
lslx
tmpa
col
restore value
set up column ctr.
shift columns
branch if have column
nxtc
try next column
AN991/D
Code Listings
0175
0176
0177
0178
0179
0180
0181
0182
0183
0184
0185
0186
0187
0188
0189
0190
0191
0192
0193
0194
0195
0196
0197
0198
0199
0200
0201
0202
0203
0204
0205
0206
0207
0208
0209
0210
0211
0212
0213
0214
0215
0216
0217
0218
0219
0220
0221
0222
0223
0224
0225
0226
0227
0228
0229
0230
0231
0232
0233
0234
0235
01AD
01AE
01AF
01B1
01B2
01B4
01B6
58
9F
BB B0
97
E6 20
B7 B1
81
lslx
txa
add
tax
lda
sta
rts
rwno
kypd,x
tmpa
x=4*col. no.
place x in a
key value =4*col + row
place a in x
convert to decimal
****** temperature conversion routine ******
*
* farenheit value is received from 705r3 via
* spi and received in the a register. the value
* is converted to celcius and the leftmost
* led is blanked.
01B7
01B7
01BA
01BC
01BE
01C0
01C1
01C3
r3int
CD
B6
A0
24
40
AE
BF
01 61
0C
20
05
0A
B6
equ
jsr
lda
sub
bhs
nega
ldx
stx
*
spird
spdr
#$20
conv
#$0a
base+2
read value
transfer value to register
subtract 32
if pos. convert
negate
‘-’ pattern
*** temperature conversion ***
** a 16-bit multiply by 5 is performed on the
** value received from the r3. this number
** is then divided by 9.
01C5
01C7
01C9
01CB
01CC
01CE
01CF
01D1
01D3
01D5
01D7
01D9
01DB
01DC
01DE
01E0
01E2
01E4
01E6
01E8
01EA
01EC
01EE
3F
3F
B7
48
39
48
39
BB
24
3C
3F
B7
98
3C
B7
B6
A2
B7
B6
A0
24
3D
26
B9
B8
B8
conv
B9
B9
B8
02
B9
B2
B8
B2
B8
B9
00
B9
B8
09
F0
B9
EC
div
nxt9
clr
clr
sta
lsla
rol
lsla
rol
add
bcc
inc
clr
sta
clc
inc
sta
lda
sbc
sta
lda
sub
bcc
tst
bne
msb
lsb
lsb
msb
msb
lsb
div
msb
dctr
lsb
dctr
lsb
msb
#$00
msb
lsb
#$09
nxt9
msb
nxt9
clear counters
multiply by 2
load overflow into msb
multiply by 2
load overflow into msb
a contains value x5
if overflow, inc msb
subtract borrow from msb
count factors of 9
if no borrow, repeat
if borrow, check for end
repeat if not end
*** end of divide, add last 9 back in and
*** check remainder for rounding
01F0
01F2
01F4
01F6
AB
A1
22
3A
09
04
02
B2
add
cmp
bhl
dec
#$09
#$04
done
dctr
find remainder
if greater
then 4, round up
17
AN991/D
0236
0237
0238
0239
0240
0241
0242
0243
0244
0245
0246
0247
0248
0249
0250
0251
0252
0253
0254
0255
0256
0257
0258
0259
0260
0261
0262
0263
0264
0265
0266
0267
0268
0269
0270
0271
0272
0273
0274
0275
0276
0277
0278
0279
0280
0281
0282
0283
0284
0285
0286
0287
0288
0289
0290
0291
0292
0293
0294
0295
18
01FB B6 B2
done
lda
dctr
01FA AE 0B
01FC BF B7
pos
ldx
stx
#$0b
base+3
blank pattern
blank most sig. digit
*** convert binary value to bcd value ***
*
* the x registers begins with the binary value
* and exits with zero. each digit, units, tens
* and hundreds, is stored separately and checked
* for a value equal to 10.
01FE
01FF
0200
0202
0204
0205
0207
0208
0209
020B
020D
020F
0211
0213
0215
0216
0218
021A
021C
97
4F
3F
3F
5D
27
5A
4C
A1
26
3C
B6
A1
27
4F
20
3F
3C
20
B5
B6
st
17
DA
F7
B5
B5
0A
03
zero
EC
B5
B6
F7
hund
tax
clra
clr
clr
tstx
beq
decx
inca
cmp
bne
inc
lda
cmp
beq
clra
bra
clr
inc
bra
place a into x
base+1
base+2
send
#$0a
st
base+1
base+1
#$0a
hund
st
base+1
base+2
zero
clear values
check for end
if complete, send to r3
decrement hex number
increment decimal number
equal to 10?
no, keep going
increment tens
test for 10
if equal, set hundreds
clear ones
count next 10
clear tens
increment hundreds
* send all digits to 70r3 via spi
* start by interrupting r3 and then
* sequentially sending four values
021E
0220
0222
0224
0226
0229
022A
022C
022E
022F
0231
0233
B7
B6
27
E6
CD
5C
A3
26
80
A6
B7
2D
B4
B6
0B
B4
01 59
send
nxtdg
03
F6
0B
B6
EF
blk
sta
lda
beq
lda
jsr
incx
cpx
bne
rtl
lda
sta
bra
base
base+2
blk
base,x
spiwr
store ones
#$03
nxtdg
look for end
if no, next digit
start at base
send to r3
#$06
base+2
nxtdg
*** initialize interrupt vectors ***
1FF4
1FF4
1FF6
1FF8
1FFA
1FFC
1FFE
01
01
01
01
01
01
00
00
00
B7
00
00
spivec
scivec
tmrvec
irqvec
swivec
reset
org
#1ff4
fdb
fdb
fdb
fdb
fdb
fdb
start
start
start
r3int
start
start
AN991/D
Code Listings
0001
0002
0003
0004
0005
0006
0007
0008
0009
0010
0011
0012
0013
0014
0015
0016
0017
0018
0019
0020
0021
0022
0023
0024
0025
0026
0027
0028
0029
0030
0031
0032
0033
0034
0035
0036
0037
0038
0039
0040
0041
0042
0043
0044
0045
0046
0047
0048
0049
0050
0051
0052
nam r3disp
************ REGISTER DEFINITION ************
0001
0002
0005
0006
0008
0009
000E
000F
portb
portc
ddrb
ddrc
tdr
tcr
acr
arr
0040
0040
0041
0042
0043
0044
0045
0046
0047
0048
0049
004A
wrdat
timtmp
ct
ct1
result
res1
bitct
sec
segmnt
pm
base
equ
equ
equ
equ
equ
equ
equ
equ
1
2
5
6
8
9
14
15
org
$40
rmb
rmb
rmb
rmb
rmb
rmb
rmb
rmb
rmb
rmb
rmb
1
1
1
1
1
1
1
1
1
1
4
0080
org
$80
*** display look-up table ***
0080
0080
0081
0082
0083
0084
0085
0086
0087
0088
0089
008A
008B
008C
008D
0090
01
4F
12
06
4C
24
20
0F
00
0C
7E
7F
7F
18
segtab equ
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
fcb
org
*
%00000001
%01001111
%00010010
%00000110
%01001100
%00100100
%00100000
%00001111
%00000000
%00001100
%01111110
%01111111
%01111111
%00011000
$90
0
1
2
3
4
5
6
7
8
9
blank
pm
p
program start
19
AN991/D
0053
0054
0055
0056
0057
0058
0059
0060
0061
0062
0063
0064
0065
0066
0067
0068
0069
0070
0071
0072
0073
0074
0075
0076
0077
0078
0079
0080
0081
0082
0083
0084
0085
0086
0087
0088
0089
0090
0091
0092
0093
0094
0095
0096
0097
0098
0099
0100
0101
20
*** initialize variables ***
0090
0090
0092
0095
0097
0099
009B
009D
009F
00A1
00A3
00A5
00A7
00A9
00AB
00AD
00AF
00B1
00B3
00B5
00B7
00B9
00BB
00BD
00BF
start
A6
C7
A6
B7
B7
B7
B7
B7
B7
A6
B7
B7
A6
B7
A6
B7
3F
3F
3F
A6
B7
A6
B7
9A
07
0F 38
FF
05
08
4A
4B
4C
4D
EF
02
48
CF
06
0F
09
41
47
49
3B
42
08
43
equ
lda
sta
lda
sta
sta
sta
sta
sta
sta
lda
sta
sta
lda
sta
lda
sta
clr
clr
clr
lda
sta
lda
sta
cli
*
#$07
$f38
#$ff
ddrb
tdr
base
base+1
base+2
base+3
#$ef
portc
segmnt
#$cf
ddrc
#$0f
tcr
timtmp
sec
pm
#$3b
ct
#$08
ctl
set MOR
set up port b as output
set timer for prescale of 128
blank time display
set portc to choose msd
set up c0-3, c6, c7 as outputs
unmask timer interrupt
start with time disp.
set seconds to zero
start with am
set up timing loops
* delay for
00C0
00C2
00C4
00C5
00C7
00C8
AE
A6
4A
26
5A
26
FF
FF
FD
F8
dlay
ldx
lda
deca
bne
decx
bne
#$ff
#$ff
dlay+4
dlay+2
* temperature measurement *
00CA
00CC
00CE
00D0
00D2
00D4
00D6
00D8
00DA
3F
B6
2A
B6
A2
B7
B6
A1
26
0E
0E
FC
0F
30
45
41
07
E4
clr
lda
bpl
lda
sbc
sta
lda
cmp
bne
acr
acr
*-2
arr
#$30
res1
timtmp
#$07
dlay
clear conv. complete flag
get result
adjust so 0 deg =$30
store in spi data register
check for temp. update
AN991/D
Code Listings
0102
0103
0104
0105
0106
0107
0108
0109
0110
0111
0112
0113
0114
0115
0116
0117
0118
0119
0120
0121
0122
0123
0124
0125
0126
0127
0128
0129
0130
0131
0132
0133
0134
0135
0136
0137
0138
0139
0140
0141
0142
0143
0144
0145
0146
0147
0148
0149
0150
0151
0152
0153
0154
0155
***
*
*
*
00DC
00DD
00DF
00E2
send temperature value to hc05c4 for
conversion into celcius. start by
interrupting the hc05c4 and then transmit
data via the spi.
9B
1F 02
CD 01 18
AE 04
sei
bclr
jsr
ldx
7,portc
spiwr
#$04
interrupt hc05c4
write data to hc05c4
* wait for return data ~ 140 cycles *
00E4
00E6
00E8
00EA
00EB
A6
B7
A6
4A
26
0B
51
0E
timlp
FD
lda
sta
lda
deca
bne
#$0b
base+7
#$0e
timlp
* get decimal values in celcius from
* hc05c4
00ED
00F0
00F2
00F4
00F5
00F7
00F9
00FA
CD
B6
E7
5C
A3
26
9A
20
01 01
44
4A
nxtdg
07
F4
C4
jsr
lda
sta
incx
cpx
bne
cli
bra
spird
result
base,x
#$07
nxtdg
get value
store
check for end
dlay
** select temperature display **
00FC A6 07
00FE B7 41
0100 80
temp
lda
sta
rti
#$07
timtmp
choose temp. display
**** spi routines ****
* the three pins used for the spi are
*
miso bit 6, portc
*
mosi bit 5, portc
*
sck
bit 4, portc
* the r3 waits for a high-to-low
* transition on he spi clock, which
* is provided by the hc05c4 and sent
* on portc pin 4. a bit of data is
* transferred on each high-to-low
* transition of the clock.
* spi read *
0101
0101 A6 08
0103 B7 46
spird
equ
lda
sta
*
#$08
bitct
set bit counter
21
AN991/D
0156
0157
0158
0159
0160
0161
0162
0163
0164
0165
0166
0167
0168
0169
0170
0171
0172
0173
0174
0175
0176
0177
0178
0179
0180
0181
0182
0183
0184
0185
0186
0187
0188
0189
0190
0191
0192
0193
0194
0195
0196
0197
0198
0199
0200
0201
0202
0203
0204
0205
0206
0207
0208
0209
0210
22
0105 08 02 FD
0108 0A 02 00
010B
010D
010F
0110
0112
0113
0115
0117
39
A6
4A
26
9D
3A
26
81
44
02
FD
46
EE
nxt
brset
brset
4,portc,*
5,portc,str
wait for clock transition
check data status
*
* note: the brset command automatically
* sets the carry bit to be equal to the
* bit under test
*
str
rol
result
store in result
lda
#$02
delay loop
stall
deca
bne
stall
nop
dec
bitct
check for end of byte
bne
nxt
get next bit
rts
* spi write *
* data to be sent is in result at
* start of write
0118
0118
011A
011C
011E
0120
0122
0124
0126
0127
0128
012B
012D
012F
0131
A6
B7
39
25
1D
1E
19
9D
9D
08
3A
26
1E
81
08
46
45
12
02
02
02
spiwr
02 FD
46
ED
02
tst
0132
0134
0136
0138
1C
1E
18
20
02
02
02
EE
set1
agn
equ
lda
sta
rol
bcs
bclr
bset
bclr
nop
nop
brset
dec
bne
bset
rts
*
#$08
bitct
res1
set1
6,portc
7,portc
4,portc
bset
bset
bset
bra
6,portc
7,portc
4,portc
tst
4,portc,*
bitct
agn
7,portc
set bit counter
shift data
check data status
if 0, clear miso
clear interrupt
timing delay.
wait for clock trans.
check for end of byte
clear interrupt
if 1, set miso
clear interrupt
** initialization of data read via spi **
*
* a data read is initiated via an interrupt
* from the hc05c4. the value received is
* tested to determine which function is
* requested and the processor jumps to the
* proper routine.
*
013A
013D
013F
0141
0143
CD
A6
B7
B6
A1
01 01
03
41
44
0A
c4int
jsr
lda
sta
lda
cmp
spird
#$03
timtmp
result
#$0a
get value
choose time
check for disp temp
AN991/D
Code Listings
0211
0212
0213
0214
0215
0216
0217
0218
0219
0220
0221
0222
0223
0224
0225
0226
0227
0228
0229
0230
0231
0232
0233
0234
0235
0236
0237
0238
0239
0240
0241
0242
0243
0244
0245
0246
0247
0248
0249
0250
0251
0252
0253
0254
0255
0256
0257
0258
0259
0260
0261
0262
0263
0145
0147
0149
014B
014D
014F
0151
0153
0155
0157
0159
015B
015D
27
A1
27
A1
27
A1
27
A1
27
A1
26
A6
B7
B5
0F
3C
0E
39
0D
0C
0B
6A
0C
39
FF
49
beq
cmp
beq
cmp
beq
cmp
beq
cmp
beq
cmp
bne
lda
sta
temp
#$0f
rtry
#$0e
clrtm
#$0d
am
#$0b
dsec
#$0c
dig
#$ff
pm
check for display time
check for set time
check for am
check for secs
check for pm
no, set digit
set pm address
** check for valid input **
015F
0161
0163
0165
0167
0169
016B
016D
016F
0171
0173
B6
27
A1
27
A1
26
A6
B7
B6
A1
22
4D
08
01
46
0B
48
0B
4D
4B
05
3E
am
blhr
mtn
lda
beq
cmp
beq
cmp
bne
lda
sta
lda
cmp
bhi
base+3
blhr
#$01
twoc
#$0b
blank
#$0b
base+3
base+1
#$05
blank
check tens of hours
if zero, blank digit
look for blank
if not, blank display
blank tens of hours
check tens of minutes
check against 5
if greater, blank display
* valid input, set timer counter *
0175
0177
0179
017B
017D
017F
0181
0183
0185
0187
A6
B7
A6
B7
A6
B7
3F
3F
3F
80
0F
09
43
42
06
43
47
52
53
rtry
lda
sta
lda
sta
lda
sta
clr
clr
clr
rti
#$0f
tcr
#$43
ct
#$06
ct1
sec
base+8
base+9
unmask timer interrupt
load inner loop counter
load outer loop counter
* clear displays *
0188
018A
018C
018E
0190
0192
A6
B7
B7
B7
B7
20
0B
4A
4B
4C
4D
F3
clrtm
lda
sta
sta
sta
sta
bra
#$0b
base
base+1
base+2
base+3
rtry
* input digit *
23
AN991/D
0264
0265
0266
0267
0268
0269
0270
0271
0272
0273
0274
0275
0276
0277
0278
0279
0280
0281
0282
0283
0284
0285
0286
0287
0288
0289
0290
0291
0292
0293
0294
0295
0296
0297
0298
0299
0300
0301
0302
0303
0304
0305
0306
0307
0308
0309
0310
0311
0312
0313
0314
0315
0316
0317
0318
0319
24
*** time setting routine ***
* time is inputted left to right
* and the end of input is indicated
* by pressing either the am or pm
* button. pm is denoted on the
* display by lighting the decimal
* point. counters are set to zero out
* after each second.
*
0194
0195
0197
0199
019B
019D
019F
01A1
01A3
01A5
01A7
01A9
01AB
9A
B6
B7
B6
B7
B6
B7
B6
B7
A1
22
B7
20
dig
4C
4D
4B
4C
4A
4B
44
4A
09
DE
4A
DA
cli
lda
sta
lda
sta
lda
sta
lda
sta
cmp
bhi
sta
bra
base+2
base+3
base+1
base+2
base
base+1
result
base
#$09
rtry
base
rtry
shift data left one
digit
enter digit 1
check for valid digit
get next number
* check if time less than 12 o’clock
* blank display if not
01AD
01AF
01B1
01B3
01B5
01B7
01B9
01BB
01BD
01BF
01C1
01C3
01C5
01C7
B6
A1
23
3F
3F
A6
B7
A6
B7
20
4C
02
BC
4D
4C
0D
4B
05
A4
C6
B7 41
B7 55
B7 54
80
twoc
blank
lda
cmp
bls
clr
clr
lda
sta
lda
sta
bra
base+2
#$02
mtn
base+3
base+2
#$0d
base+1
#$05
base
rtry
**** seconds display ****
* blank first two leds
*
dsec
sta
timtmp
sta
base+$b
sta
base+$a
rti
check hours units
okay, check tens of min.
send error message
set timtmp to $0b
blank 1st two leds
**** display routine ****
*
* displays are refreshed every msec
* when a timer interrupt occurs. the
* most significant digit is displayed
* first. at the conclusion of each
* minute, the time is updated
*
AN991/D
Code Listings
0320
0321
0322
0323
0324
0325
0326
0327
0328
0329
0330
0331
0332
0333
0334
0335
0336
0337
0338
0339
0340
0341
0342
0343
0344
0345
0346
0347
0348
0349
0350
0351
0352
0353
0354
0355
0356
0357
0358
0359
0360
0361
0362
0363
0364
0365
0366
0367
0368
0369
0370
0371
0372
0373
01C8
tmrint equ
01C8
01C9
01CB
01CD
01CF
01D1
99
BE
A6
B7
36
25
01D3
01D5
01D7
01D9
01DA
01DD
01DF
01E0
01E3
01E5
01E6
01E9
01EB
01ED
01EE
01F0
01F2
01F4
A6
B7
E6
5A
02
E6
5A
04
E6
5A
06
E6
A4
97
EE
BF
B6
B7
sec
ldx
lda
sta
ror
bcs
41
FF
01
48
04
F7
48
4A
min2
48 02
4A
hrs1
48 02
4A
hrs2
48 02
4A
0F
disp
80
01
48
02
lds
sta
lda
decx
brset
lda
decx
brset
lda
decx
brset
lda
and
tax
ldx
stx
lda
sta
*
timtmp
#$ff
portb
segmnt
min2
choose time or temp
blank displays
send to leds
select display
look for restart
#$f7
segmnt
base,x
restart with msd
1,segment,hrs1
base,x
2,segment,hrs2
base,x
3,segment,disp
base,x
#$0f
segtab,x
portb
segmnt
portc
load a with minutes
point to next digit
check hours units
load a with tens of min.
point to next digit
check tens of hrs.
load a with hours units
point to next digit
display value
load a with tens of hrs
mask upper nibble
set x equal to a
display value table
enable display drivers
enable display
** count display refreshes. 402 refreshes
* equals one second. after 402 refreshes,
* update clock
*
01F6
01F8
01FA
01FC
01FE
0200
0202
0204
0206
0208
020A
A6
B7
A6
B7
3A
26
A6
B7
3A
27
80
10
08
0F
09
42
08
3B
42
43
01
ret
lda
sta
lda
sta
dec
bne
lda
sta
dec
beq
rti
#$10
tdr
#$0f
tcr
ct
ret
#$3b
ct
ct1
tmchg
set timer to interrupt
after 2048 cycles
reset timer interrupt flag
decrement inner loop
reset inner loop
decrement outer loop
if one sec., to time change
***** time change routine *****
* when 60 seconds are counted,
* increase minutes by one, if
* necessary, blank minutes and increase
* hours. change am/pm if needed.
*
25
AN991/D
0374
0375
0376
0377
0378
0379
0380
0381
0382
0383
0384
0385
0386
0387
0388
0389
0390
0391
0392
0393
0394
0395
0396
0397
0398
0399
0400
0401
0402
0403
0404
0405
0406
0407
0408
0409
0410
0411
0412
0413
0414
0415
0416
0417
0418
0419
0420
0421
0422
0423
0424
0425
0426
26
020B
020B
020D
020F
0211
0213
0215
0217
0219
021B
021D
021F
0221
0223
0225
0227
0229
022B
022D
022F
0231
0233
0235
0237
0239
023B
023D
023F
0241
0243
0245
0247
0249
024B
tmchg
3C
3C
B6
A1
27
A6
B1
26
3F
3F
B6
A1
26
3F
B6
A1
26
3F
B6
A1
27
B6
A1
26
A6
B7
A6
B7
20
3C
20
3C
20
47
52
52
0A
38
3C
47
54
47
53
4A
09
20
4A
4B
05
1C
4B
4D
0B
1E
4C
02
2A
0B
4D
01
4C
2A
4A
26
4B
22
024D 3F 52
024F 3C 53
0251 20 C2
minck
inm1
inm2
tens
equ
inc
inc
lda
cmp
beq
lda
cmp
bne
clr
clr
lda
cmp
bne
clr
lda
cmp
bne
clr
lda
cmp
beq
lda
cmp
bne
lda
sta
lda
sta
bra
inc
bra
inc
bra
*
sec
base+8
base+8
#$0a
tens
#$3c
sec
ret1
sec
base+9
base
#$09
inm1
base
base+1
#$05
inm2
base+1
base+3
#$0b
hrck
base+2
#$02
inhr1a
#$0b
base+3
#$01
base+2
ret1
base
ret1
base+1
ret1
clr
inc
bra
base+8
base+9
minck
increase seconds
inc. secs. units
look for ten
if yes, inc. tens
look for a minute
wait for next second
zero display
check min. units
less than 9?
increase
min. units = 0
check tens of min.
less than 5?
increase
tens of min =0
check tens of hrs.
look for blank
less than 10:00
check hrs. units
less than 2?
increase
set time to 1:00
done
increase min. units
done
increase tens of min.
zero sec. units
inc sec. tens
* increase hours *
0253
0255
0257
0259
025B
025D
025F
0261
0263
0265
0267
0269
B6
A1
26
3F
3F
3C
20
3C
20
3C
B6
A1
4C
09
08
4C
4D
4D
0E
4C
0A
4C
4C
02
hrck
lda
cmp
bne
clr
clr
inc
bra
inhr1
inc
bra
inhr1a inc
lda
cmp
base+2
#$09
inhr1
base+2
base+3
base+3
ret1
base+2
ret1
base+2
base+2
#$02
check hours units
less than 9?
increase
hours units =0
tens of hours =1
done
increase hours units
done
increase hours units
check value
for 12:00
AN991/D
Code Listings
0427
0428
0429
0430
0431
0432
0433
0434
0435
0436
0437
0438
0439
0440
0441
0442
0443
026B
026D
026F
0271
0273
0275
0277
26
33
A6
B7
A6
B7
80
9D
49
3B
42
08
43
ret1
bne
com
lda
sta
lda
sta
rti
ret
pm
#$3b
ct
#$08
ct1
no, done
switch pm indicator
reset inner loop counter
reset outer loop counter
*** initialize interrupt vectors ***
0FF8
0FF8
0FFA
0FFC
0FFE
01
01
00
00
C8
3A
90
90
tmrvec
intveq
swiveq
reset
org
$ff8
fdb
fdb
fdb
fdb
tmrint
c4int
start
start
27
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AN991/D

Using the Serial Peripheral Interface to Communicate

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