KEYSCN2
In February 2020 I wrote keyscn, a quick and dirty chunk of 6809 assembly to scan the CoCo keyboard and display them, similar to a keyboard diagnostic.
What I built was a two-pass driver:
- Pass 2 works through the 8 stored port B values (the 7 row values from each of the 8 strobes) and decodes the key to a screen address
While that works like a champ and was great for validating I could read any combination of keys I liked, it also has problems:
- It takes nearly a KB of RAM for the code
- It's a huge wall of cut and paste code with a little data change in each block
- It only works for Color Computer keyboard layout, not Dragon
- It doesn't really handle the case of joystick buttons versus keyboard inputs
I really want a nice keyboard driver so I am revisiting and reimplementing a keyboard scanner from the ground up.
TL;DR
I'll save you a lot of headache trying to follow my mental meanderings:
If you're looking for a keyboard scanning routine with bells and whistles that isn't POLCAT, take a stroll over the Sixxie's Dragon subsite and check out his keyboard.s:
http://www.6809.org.uk/dragon/
Sixxie knows a thing or two about the Dragon and CoCo family so its worth a look …
STILL HERE?
I am keeping the two-pass design, but replacing the unrolled loop for the PIA polling with a small ROR loop.
ROR OR ROL?
The pass 1 polling code is KEYSCN is down to 24 bytes of code from 99 bytes of code used in the previous version.
Along the way I discovered why POLCAT used ROL in stead of ROR in its loop shift…
The pass 1 loop samples the PIA 8 times, reading a whole column of key data at a time.
With ROR the key matrix has to be decoded right to left, top to bottom (KEYBUF + 7 to KEYBUF + 0) to get a 0-55 key value:
| ROW 7 | ROW 6 | ROW 5 | ROW 4 | ROW 3 | ROW 2 | ROW 1 | ROW 0 | ADDRESS |
|---|---|---|---|---|---|---|---|---|
| SHIFT | / | , | SPACE | W | O | G | KEYBUF + 0 | |
| F2 | ? | 6 | RIGHT ARROW | V | N | F | KEYBUF + 1 | |
| F1 | - | 5 | LEFT ARROW | U | M | E | KEYBUF + 2 | |
| CTRL | , | 4 | DOWN ARROW | T | L | D | KEYBUF + 3 | |
| ALT | ; | 3 | UP ARROW | S | K | C | KEYBUF + 4 | |
| BRK | : | 2 | Z | R | J | B | KEYBUF + 5 | |
| CLR | 9 | 1 | Y | Q | I | A | KEYBUF + 6 | |
| ENTER | 8 | 0 | X | P | H | @ | KEYBUF + 7 |
With ROL, the key matrix can be decoded bottom to top (KEYBUF +0 to KEYBUF + 7) instead.
| ROW 7 | ROW 6 | ROW 5 | ROW 4 | ROW 3 | ROW 2 | ROW 1 | ROW 0 | ADDRESS |
|---|---|---|---|---|---|---|---|---|
| ENTER | 8 | 0 | X | P | H | @ | KEYBUF + 0 | |
| CLR | 9 | 1 | Y | Q | I | A | KEYBUF + 1 | |
| BRK | : | 2 | Z | R | J | B | KEYBUF + 2 | |
| ALT | ; | 3 | UP ARROW | S | K | C | KEYBUF + 3 | |
| CTRL | , | 4 | DOWN ARROW | T | L | D | KEYBUF + 4 | |
| F1 | - | 5 | LEFT ARROW | U | M | E | KEYBUF + 5 | |
| F2 | ? | 6 | RIGHT ARROW | V | N | F | KEYBUF + 6 | |
| SHIFT | / | , | SPACE | W | O | G | KEYBUF + 7 |
And pass 2 needed to be completely rebuilt and rethought to allow for CoCo or Dragon decoding without using nearly a KB of copy-paste code with minor changes.
The example code below polls the keys and store the raw polled data directly to video screen.
Row one shows 9 orange blocks, one for joybuf and each of the 8 rows of the keybuf scan matrix.
The orange block is the semigraphics character for a value or 255 which means no keys were pressed in that column strobe.
Pressing a key will bring a bit low which will shown as one quarter of block disappearing, or the block changing colors.
Pressing joystick buttons show more interesting patterns as it activates the entire row at once.
DECODING
Row two shows the decoded key.
The decoding is essentially an inner and outer loop.
The outer loop steps through each of the 8 bytes samples from strobing each column of the keyboard matrix.
The inner loop steps bit-by-bit though the sampled byte.
The B register is being incremented by 8 for each bit to act as a “cursor” stepping through the sampled PIA data.
So, B starts at 0, then goes to 8, 16, 24, 32, 40, 48, and when it hits 56 those 7 bits read from the PIA have been handled.
Then we subtract 55 which leaves B at 1 for the start of the next column of sampled data, rather than 0.
The reason for the funky stepping is to convert the sampled 56 bit pattern into a linear offset into a key decoding table which I can switch between CoCo and Dragon versions as needed.
The pshs a/puls a is a cheap hack to get a display where I just call an address table and plonk the character decoded from the B-register decoded and the current keyboard table onto the screen.
I've marked the start and end off the cheap “show a key on screen in a keyboard-like pattern” sort of like the Tandy Diagnostic cartridge display.
If you just want to return the key, then branch to DECD030 goes here instead.
I went with this design to also allow for additional key tables and functions such as different tables for unshifted, shifted, control, and alt key combinations to all be handled differently if I wanted.
This design also allows for direct sampling of any combination of keys active at once supported by the matrix itself.
SAVINGS
This version is now 492 bytes of code and data, including the Dragon key decoding, rather than 979 for just CoCo key decoding - a ~50% space savings while more than doubling the features.
Compared to POLCAT this thing is still blazing fast just like keyscn.
The biggest delay is a completely optional DELAY loop called in the screen display just to give us time to see the key on the screen before blanking it again.
In usage, I would probably call KEYSCN at the end of each display field.
That would sample the joystick buttons and keys up/down at a 50 or 60Hz frequency.
Then, in the main game loop, check the JOYBUF and KEYBUF for any desired button presses, all the way up to using DECODE to pull everything active into a larger typing buffer or some such.
DISCUSSION
Please feel free to discuss this code with me on the Tandy Radio Shack Color Computer Discord in the PROGRAMMING / #assembly channel
KEYSCN2.ASM
For Color Computer 1, 2, 3, and Dragon 32 or 64 with 4K or more.
;*********************************************************************
;* Title: KEYSCN2
;*********************************************************************
;* Author: R. Allen Murphey
;*
;* License:
;* Copyright (c) 2022 R. "Allen" Murphey aka "Exile In Paradise"
;* Released to you under Creative Commons Attribution-Share Alike (CC-BY-SA)
;* Additional/other licenses possible by request.
;*
;* Description: Color Computer and Dragon keyboard driver
;*
;* Documentation:
;* https://exileinparadise.com/tandy_color_computer:keyscn2
;* https://exileinparadise.com/tandy_color_computer:keyscn
;*
;* Include Files: none
;*
;* Assembler: lwasm from LWtools 4.19+
;*
;* Revision History:
;* Rev # Date Who Comments
;* ----- ----------- ------ ---------------------------------------
;* 00 2022 RAM Created initial file
;*********************************************************************
VIDRAM: equ $0400 ; start of video memory
JOYBUF: equ $0400 ; just store stuff on the screen for now
KEYBUF: equ $0401 ; just store more on the screen for now
PIA0AD: equ $FF00 ; PIA0 port A data = keyboard row inputs
PIA0BD: equ $FF02 ; PIA0 port B data = keyboard column strobe out
RESET: equ $FFFE ; Address of MPU Reset Vector
VECCOCO: equ $A027 ; CoCo 1/2 reset vector value
VECDRGN: equ $B3B4 ; Dragon32/64 reset vector value
VECCOCO3: equ $8C1B ; CoCo3 reset vector value
KEY_UP: equ 27
KEY_DOWN: equ 28
KEY_LEFT: equ 29
KEY_RIGHT: equ 30
KEY_ENTER: equ 48
KEY_CLEAR: equ 49
KEY_BREAK: equ 50
KEY_ALT: equ 51
KEY_CTRL: equ 52
KEY_F1: equ 53
KEY_F2: equ 54
KEY_SHIFT: equ 55
org $0E00 ; some place to live
INIT:
bsr CLS ; clear screen
ldx RESET ; Get RESET vector
cmpx #VECDRGN ; if Dragon
beq CFGDRGN ; swap keymaps
; fallthru for CoCo1/2/3
CFGCOCO:
ldx #COCOKEYS ; get address of CoCo key table
stx KEYTABLE ; set the pointer
ldx #COCOPOS ; get address of CoCo screen addrs
stx POSTABLE ; set that point
bra MAIN ; configured, lets go!
CFGDRGN:
ldx #DRGNKEYS ; get address of CoCo key table
stx KEYTABLE ; set the pointer
ldx #DRGNPOS ; get address of CoCo screen addrs
stx POSTABLE ; set that point
; fallthru to MAIN
MAIN:
bsr KEYSCN ; poll keys
bsr DECODE ; can we find the key?
bra MAIN ; endless loop
CLS:
pshs X,D,CC ; save our registers
ldd #$8080 ; fade to black
ldx #VIDRAM ; point to start of video memory
CLS010: std ,X++ ; clear two characters
cmpx #VIDRAM+512 ; reached end of video memory?
bne CLS010 ; go back
puls X,D,CC,PC ; restore registers and bail
DELAY:
pshs X,CC ; save our registers
ldx #$045E ; some delay
DELAY010: leax -1,X ; countdown X
bne DELAY010 ; done counting?
puls X,CC,PC ; restore registers and bail
KEYSCN:
pshs X,A,CC ; save our registers
ldx #JOYBUF ; point to place to save polled data
lda #$FF ; all bits high
sta PIA0BD ; disable all keyboard column strobes
andcc #%11111110 ; CLC clear carry
KEY010: lda PIA0AD ; read the keyboard rows, first joy, then keys
sta ,X+ ; store to pointer and advance to next save ptr
rol PIA0BD ; move the zero bit right to strobe next column
bcs KEY010 ; keep reading until we hit our original CLC
puls X,A,CC,PC ; restore registers and bail
DECODE:
pshs A,B,X,Y,CC ; save our registers
ldx #KEYBUF ; pointer to where we saved PIA data
ldy KEYTABLE ; load Y with ptr to keys read in
clrb ; start with b empty as bit cursor
DECD000: lda ,X+ ; get read key bits into A to process
DECD010: rora ; move low bit into carry to test
bcs DECD020 ; bit high, key not processed, skip lookup
; This next bit is our cheesy keyboard display
; Replace this with whatever you want to do
; with a key in B
pshs A,X,CC ; stash A,X,CC for a couple of opcodes...
ldx POSTABLE ; get pointer to screen position table
tfr B,A ; copy B key index into A ...
asla ; to multiply by two for use as ...
leax A,X ; the offset into the 2-byte address table
lda B,Y ; get the key pressed [0-55]
sta [,X] ; put on screen at address from *POS table
jsr DELAY ; hang around for a while so we can see it
lda #$80 ; load up a black block
sta [,X] ; put on screen over the key shown
puls A,X,CC ; clean up registers and fall through
; end of sample display code
DECD020: addb #8 ; move bit cursor to next column
cmpb #56 ; have we read past bit 6 of keybuf?
blt DECD010 ; no go get next key bit from current buffer
subb #55 ; yes, go back to row 0 of next column
cmpb #8 ; is bit cursor past end of column data?
blt DECD000 ; no go get next key buffer and decode it
DECD030: puls A,B,X,Y,CC,PC ; restore registers and bail
COCOKEYS: fcb '@','A','B','C','D','E','F','G'
fcb 'H','I','J','K','L','M','N','O'
fcb 'P','Q','R','S','T','U','V','W'
fcb 'X','Y','Z',KEY_UP,KEY_DOWN,KEY_LEFT,KEY_RIGHT,' '
fcb '0','1','2','3','4','5','6','7'
fcb '8','9',':',';',',','-','.','/'
fcb KEY_ENTER,KEY_CLEAR,KEY_BREAK,KEY_ALT,KEY_CTRL,KEY_F1,KEY_F2,KEY_SHIFT
COCOPOS:
fdb $0478,$04A5,$04EE,$04EA,$04A9,$0468,$04AB,$04AD
fdb $04AF,$0472,$04B1,$04B3,$04B5,$04F2,$04F0,$0474
fdb $0476,$0464,$046A,$04A7,$046C,$0470,$04EC,$0466
fdb $04E8,$046E,$04E6,$047C,$04FC,$04BB,$04BD,$052F
fdb $0435,$0423,$0425,$0427,$0429,$042B,$042D,$042F
fdb $0431,$0433,$0437,$04B7,$04F4,$0439,$04F6,$04F8
fdb $04B9,$047A,$043D,$0462,$04A3,$053B,$053D,$04E4
DRGNKEYS: fcb '0','1','2','3','4','5','6','7'
fcb '8','9',':',';',',','-','.','/'
fcb '@','A','B','C','D','E','F','G'
fcb 'H','I','J','K','L','M','N','O'
fcb 'P','Q','R','S','T','U','V','W'
fcb 'X','Y','Z',KEY_UP,KEY_DOWN,KEY_LEFT,KEY_RIGHT,' '
fcb KEY_ENTER,KEY_CLEAR,KEY_BREAK,KEY_ALT,KEY_CTRL,KEY_F1,KEY_F2,KEY_SHIFT
DRGNPOS:
fdb $0435,$0423,$0425,$0427,$0429,$042B,$042D,$042F
fdb $0431,$0433,$0437,$04B7,$04F4,$0439,$04F6,$04F8
fdb $0478,$04A5,$04EE,$04EA,$04A9,$0468,$04AB,$04AD
fdb $04AF,$0472,$04B1,$04B3,$04B5,$04F2,$04F0,$0474
fdb $0476,$0464,$046A,$04A7,$046C,$0470,$04EC,$0466
fdb $04E8,$046E,$04E6,$047C,$04FC,$04BB,$04BD,$052F
fdb $04B9,$047A,$043D,$0462,$04A3,$053B,$053D,$04E4
KEYTABLE rmb 2 ; pointer to CoCo or Dragon key decode table
POSTABLE rmb 2 ; pointer to CoCo or Dragon screen addresses
end INIT
;*********************************************************************
;* End of keyscn2.asm
;*********************************************************************
SEE ALSO
Color Computer Technical Reference Manual
SAMS Computerfacts: Color Computer
Color Computer 2 Service Manual
SAMS Computerfacts Color Computer 2
RTS
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