PLEASE NOTE: I do not sell
production boards. If you would like to buy an M62 Z80 SBC system board/parts kit,
contact Peter Murray,
Peter@39k.ca
I simply provide you with information to build
your own breadboard computer.
Overview
The
M62 CTC I/O Board can be used with either the M62 SBC or SBC2.
There is extensive information on the CTC, including interrupts in
the
Circuits section under More I/O:
Z80 CTC.
Bank Addressing
JP15
carves up the I/O space into for 64-byte blocks; they
are:
-
$00 - $3F IO_0
block
-
$40 - $7F IO_1
"
-
$80 - $BF IO_2
"
-
$C0 - $FF IO_3
"
The
Z80 assembly
code is written to support any I/O byte address between $00 and
$3F being used. With both block and byte I/O addressing being
configurable on this board, you could change it to whatever as long
as your code agrees.
Block Addressing
We
are using the IO_0 bank of I/O addresses
via the JP15 jumper between pins 1 & 2. IC1 carves that bank
of 64 into 8
blocks of 8 addresses. You can use JP1 to select whichever I/O block you
like; we have chosen $30 to $37 (there is a jumper between pins 13
and 14 of JP1) because it is not in use elsewhere in our Z80
system. This will become
CTC_CS, the chip select for the CTC.
By
using A0 and A2 as inputs to IC2A, the address outputs will be $30,
$31, $34 and $35. (We don't need $30 to $33 for the output
TONE_1 on pin 6.)
I/O
address $30 to $33 will be used by the CTC chip (via the A0 and A1
pins of the CTC) so we can access the
four timer/counter channels. Although we don't need pin 5,
TONE_2, it's there in
case you decide to do a little experimenting. (Keep in mind that it
does not have pulse stretching circuitry like
TONE_1 does.)
The
TONE_1 output
goes to the ATtiny85's pin 5, PB0, that we know as Arduino pin D0. A low
signal here
will force a tone or melody out pin 6, PB1, a.k.a. D1.
How does it work? (Summary info is found here. The gory details can
be found at
Circuits section
.)
When
an OUT instruction is sent to I/O address $30-$37, it selects the CTC so
that its inputs and outputs can become active.
The CTC
in Timer mode uses the
system CPU CLK signal on
pin 15 to countdown such that a
61Hz
signal is output on pin 7 which is Channel 0. The 7474's IC7A output
from that input divides it by 2 so we see a rapid 30Hz beat signal
from green LED1.
The
output of CTC pin 7 is jumpered to input pin 22 which is Channel 1.
In Counter mode, the output on pin 8 is a 4Hz signal to the 7474
latch whose IC7B output is a 2Hz beat signal from yellow LED2.
The
output of CTC pin 8 is jumpered to input pin 21 which is Channel 2.
In Counter mode, the output on pin 9 is a 2Hz signal to the 7474
latch whose IC8A output is a 1 Hz beat signal from red LED3; this is a
flash every second.
The
output of CTC pin 9 is jumpered to input pin 20 which is Channel 3.
(There is no output pin for this channel.) In Counter mode, it will
count down every 1 second and send an interrupt on pin 12 to the Z80.
Responding to the interrupt via its interrupt service routine, the
CPU will send a low signal to address $34 which is connected to pin 5 of the
ATtiny85. The microcontroller in turn will play a programmed
melody/tune/chirp and light up blue LED4.
More
info on interrupts can be found here in the
Circuits section.
What's with all the jumpers?
You're
probably wondering about the jumpers JP11 through JP20
in Eagle CAD: 2. Counter
Timer Circuit.
We know
we need to jumper TO0 (out) to TRG1 (in) for the 61.035Hz signal so
that's what JP15 does; you add the jumper. JP18 should be jumpered to
complete the circuit to LED1.
But you
may want to use TRG0 and TO0 for something else instead of the LED1
circuit. In that case, remove JP15 and JP18. You can use female
jumper cables to route TRG0 and TO0 at position JP11 at the board
edge to the prototyping part of the board.
You'll
need JP16 jumpered for TO1 and TRG2 for the 1Hz LED2 circuit. JP19
completes the circuit. Removing both JP16 and JP19 will give you
prototyping isolation so you can use those two signals elsewhere at
JP12 at the board edge.
You'll
need JP17 jumpered for TO2 and TRG3 for the 0.1Hz LED3 circuit.
Removing both JP17 and JP20 will give you prototyping isolation so
you can use those two signals elsewhere at the board edge.
Development space:
We have
added some prototyping space to the left side of the board along with a couple of
vertical GND and VCC lines. You can add your own devices here
without having to wire to a breadboard (unless you want to).
To Do List:
1)
Write the assembly code. The code for the configuration program and the
interrupt service routine are cumulatively small. With the
difficulty I had in getting the CTC to interrupt reliably, I ended
up writing code to a) run on boot ROM (to avoid the BIOS) as well as
b) standalone code to be
run at $4000.
2)
Program the ATtiny85 in C++ to play a tone/melody on pin 6 when it receives a low INT signal on pin 5.
You'll need a programmer like this
Sparkfun unit, or use an Arduino
UNO as the
programmer
to program the ATtiny85. Here's a doc I wrote that should
simplify that process:
Program_an_ATtiny85.txt
Where's the software?
1)
You'll need the assembly code of
CTC_4ch_1int___16a.bin to run at address
4000h that will configure the CTC. Use the ROM Monitor "X" command
to perform a File | Send File to address $4000. Follow this with "G
4000" to execute the file at that location.
2)
The ATtiny85 won't do much unless it's programmed with the
CTC_60s.ino
file.
3)
If you have issues with trying to get the magnetic buzzer/piezo to
work properly, run the assembly program
Test_IO_34h.bin at $4000 which will
send a signal directly to the ATtiny85 to play the tone.
4)
Initially I had some issues getting the CTC to run reliably so
here's some code I wrote for a boot ROM that helped with isolating
the issue:
Boot_CTC_IM2__05a.bin
5)
If you're just trying to test the buzzer, here's some effective boot
ROM code:
BOOT_CTC_IO_34h.bin
Logic Analyzer Output
Below are 4 enlargeable images showing:
1)
The red line on the left (third from the bottom) is the low-going trigger for
INT. This causes pin
5 (AR5, second from the bottom) to the Arduino ATtiny85 to go high briefly which will trigger it to
play a tone. We also see the tone being played on pin 6 (AR6, bottom) to the
"piezo" speaker.
2)
The display is zoomed a little to show the AR5 signal stretched a
bit.
3)
The display is zoomed more. The operands (green, near the top) and decodes
(purple, near the top) cannot be read yet.
4)
The display is zoomed enough to show the start of the interrupt
routine: JP 0144h, NOP, PUSH AF, LD A 00h, OUT(34h) A, and then a
short delay routine starts before LD A 01h, OUT(34h) A, EI, POP AF,
and RETI. The ATtiny85 did not seem to react well to the rapid
raising and lowering of D0 (AR5) so including the 1ms delay was
helpful.
1)
2)
3)
4)![](tn_LA_03.PNG)
Additional Info
If
you need additional info on the CTC Control Word, see page 7-60 of
Osborne_4_and_8-Bit_Microprocessor_Handbook.pdf
I
see the schematics. Where is the Bill of Materials parts list?
The
BOM is at the bottom of the adjacent panel.
How big is the CTC I/O bd. and what will the printed circuit board look like?
The
PCB measures 100mm x 100mm (4" x 4"). Click the adjacent thumbnail
to see a possible parts layouts.
Note: M62 Bus is copyrighted by Peter
Murray of Murray Electronics,
http://www.39k.ca |