Keyboard

The C64 Keyboard has 66 keys on it. Keyboard reads are done using the CIA.

Definition

The C64 is a keyboard computer, that is, a computer which is built inside a keyboard. Other homecomputers are built this way, such as Commodore VC 20, C16, C116, C128, Plus/4, Amiga or Atari ST.

The Keyboard is the main Input Device of the C64. Most typically, it is used to type BASIC-commands such as LOAD,LIST, RUN etc.

Pictures of C64 keyboards

VIC20-C64: orange functions keys

C64: grey functions keys

Aldi-C64: light grey functions keys

C64C / C64G: upper gfx chars

Keyboard Matrix

		CIA 1 Port B ($DC01)								Joy 2
		PB7	PB6	PB5	PB4	PB3	PB2	PB1	PB0
CIA1 Port A ($DC00)	PA7	STOP	Q	C=	SPACE	2	CTRL	<-	1
	PA6	/	^	=	RSHIFT	HOME	;	*	£
	PA5	,	@	:	.	-	L	P	+
	PA4	N	O	K	M	0	J	I	9	Fire
	PA3	V	U	H	B	8	G	Y	7	Right
	PA2	X	T	F	C	6	D	R	5	Left
	PA1	LSHIFT	E	S	Z	4	A	W	3	Down
	PA0	CRSR DN	F5	F3	F1	F7	CRSR RT	RETURN	DELETE	Up
Joy 1					Fire	Right	Left	Down	Up

The matrix directly covers 64 out of the 66 keys. The remaining two are Restore which is tied to the NMI line and not part of the matrix, and Shift Lock which is tied to the same wire as LSHIFT.

Programming

direct addressing of a key

; This program waits until the key "S" was pushed.
; Start with SYS 49152

*=$c000                  ; startaddress 

PRA  =  $dc00            ; CIA#1 (Port Register A)
DDRA =  $dc02            ; CIA#1 (Data Direction Register A)

PRB  =  $dc01            ; CIA#1 (Port Register B)
DDRB =  $dc03            ; CIA#1 (Data Direction Register B)


start    sei             ; interrupts deactivated

         lda #%11111111  ; CIA#1 port A = outputs 
         sta DDRA             

         lda #%00000000  ; CIA#1 port B = inputs
         sta DDRB             

         lda #%11111101  ; testing column 1 (COL1) of the matrix
         sta PRA
            
loop     lda PRB
         and #%00100000  ; masking row 5 (ROW5) 
         bne loop        ; wait until key "S" 

         cli             ; interrupts activated

ende     rts             ; back to BASIC

.c000  78         sei
.c001  a9 ff      lda #$ff
.c003  8d 02 dc   sta $dc02
.c006  a9 00      lda #$00
.c008  8d 03 dc   sta $dc03
.c00b  a9 fd      lda #$fd
.c00d  8d 00 dc   sta $dc00
.c010  ad 01 dc   lda $dc01
.c013  29 20      and #$20
.c015  d0 f9      bne $c010
.c017  58         cli
.c018  60         rts

Keyboardrequest in BASIC

• With the BASIC-Command INPUT:

10 INPUT "Write here something"; A$
20 PRINT "You write: "; A$

Remark: The keyboard input must be a confirmation by pushing the key <RETURN> to continue the program. The keyboard input is saved after the input in variable A$.

• With the BASIC-Command GET:

10 PRINT "Push a key, please:": A$ = ""
20 GET A$: IF A$="" THEN 20
30 PRINT "You push: "; A$

Remark: The keyboard input occurs key by key. Control and function keys work, too, but the screen output isn't always correct.
When no key is pressed the variable A$ gets an empty char string. For simulation a wait mode must be checked A$. Then A$ is empty, the program must be jumping to the command GET.

• With the BASIC-Command PEEK:

10 PRINT "Push a key, please:": T = ""
20 T = PEEK(197): IF T=64 THEN 20
30 PRINT "You push the key <"; CHR$(T) ;"> with the keycode: "; T

Remark: The keyboard input is occur key by key with reading the memory address 197 ($00C5).
Then not a key is pushing, is the confirmation value 64. After that (for the wait mode) must be jumping to the command PEEK.
Control and function keys can clicking, too. The screen output isn't correct, but the keycode is correct.

PEEKs & POKEs

Autorepeat:

POKE 650,128 activate the autorepeat by pushing a key for a longer time
POKE 650,0 deactivate this function.

Keyboardlock:

POKE 649,0 blocks the keyboard, because the keyboard puffer has got the length 0
POKE 649,10: POKE 808,237 deactivate the lock.

or

POKE 655,71 change the pointer of the keyboard codetable; now keyboardlock
POKE 655,72 deactivate the lock

or

POKE 56322,224 deactivated the keyboard, because the pointer of the CIA 1 is changed. This POKE is using for the joystickscans.
POKE 56322,255 activated the keyboard.

or by deactivation the interrupt (exception: <RUN/STOP>+<RESTORE>) or ports.

Deactivate separate keys:

• <RUN/STOP>: Off: POKE 788,52 - On: POKE 788,49
• <RESTORE>: Off: POKE 792,193 - On: POKE 792,234

Keyboardcache: In memory addresses 631-640 is the keyboard cache (buffer). It can store up to 10 characters and can be read from using PEEK, or written to using POKE to simulate keyboard input. Memory address 198 stores the number of characters in the keyboard cache. POKE 198,0 effectively clears the keyboard cache.

Links

Wikipedia: Keyboard_(computing)