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loop_01:
   lda keys
   bpl loop_90      ; no key pressed... 

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...
	ldy #0			; not strictly required... will get there eventually
...
  ; update the display count; we have eight leds but we only drive six
   ; to save code space (we don't need to clear them)
   iny
   cpy #6
   bne loop
   ldy #0
   bra loop
...

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	ldy #5			; NB. might actually be required,
                                        ; IF using the other two selects for something else
...
  ; update the display count; we have eight leds but we only drive six
   ; to save code space (we don't need to clear them)
   dey
   bpl loop
   ldy #5
   bra loop
... 

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VERSION = $00	; alpha, $01 is first beta release
REVISION = $01	; 2025-06-07

   ; 120 bytes, pending bug fixes
   ; * Main: 99 
   ; * to_leds: 17
   ; * Reset Vectors: 4

; NB. For hardwired hex to 6digit, 7seg display
; Character bit5 -> decimal pointer
; so DNC Q7 of translation table

; The translation table is:
;LED_CODE	db 0b00111111	;0
;		db 0b00000110	;1
;		db 0b01011011	;2
;		db 0b01001111	;3
;		db 0b01100110	;4
;		db 0b01101101	;5
;		db 0b01111101	;6
;		db 0b00000111	;7
;		db 0b01111111	;8
;		db 0b01101111	;9
;		db 0b01011111	;a
;		db 0b00111100	;b
;		db 0b00101000	;c
;		db 0b01011110	;d
;		db 0b01111101	;e
;		db 0b01110001	;f
leds = $00
data = $07
W = $08

; Paleolithic
led_addr = $0B08	; guesstimate
keys = $0B00		; guesstimate

; Neolithic		; 6 digit 14pin LED block
; led_addr = $0880	; /Y0-/Y5 decode lines
; key = $0886		; /Y6 decode line

	code
	org $ff80

start:			; +2
   ldy #5  ; Will be required if other 2 selects have different uses.
loop:			; +5
   ; for each character...
   lda leds,y
   sta led_addr,y   ; display bit pattern

loop_01:		; +5
   lda keys
   bpl loop_99      ; no key pressed...
   ; do stuff to sort out the key value

			; +20
   ; if key value = return
   cmp #RETURN
   bne loop_2
   ;   increment memory address pointer
   lda data
   sta (W)
   inc W
   bne +
   inc W+1
+  lda (W)
   sta data
   bra loop_90
   ; endif

loop_2:			; +7
   ; if key value = go
   cmp #RUN
   bne loop_3
   ;   execute the program
   jmp (W)
   ; endif

loop_3:			; +10
   ; if key value = Hi
   cmp #Hi
   bne loop_4
   LDA data
   STA W+1
   bra loop_90
   ; endif

loop_4:			; +10
   ; if key value = Lo
   cmp #Lo
   bne loop_4
   LDA data
   STA W
   bra loop_90
   ; endif
			; +14
   ; else shuffle key value into (W)
   and #$0F
   asl data
   asl data
   asl data
   asl data
   ora data
   sta data  
			; +4
loop_90:
   ; wait for key to be released
   ; this will cause display glitch, but...
   lda keys
   bmi loop_90

loop_99:		; +17
   ; put W and (W) into leds
   ; [x][x][x][x][x][x][ ][ ]
   ; (also provides a short delay for the LED multiplex)
   ldx #0
   lda W+1
   jsr to_leds
   lda W
   jsr to_leds
   lda data
   jsr to_leds

			; +5
   ; update the display count; we have eight leds but we only drive six
   ; to save code space (we don't need to clear them)
   dey
   bpl loop
   bra start

to_leds:		; +17
   ; unpack byte into two adjacent LED patterns
   ; x has character position
   pha
   and #$0f         ; low nibble
   sta leds+1,x      ; and output into the LED array
   pla
   lsr a
   lsr a
   lsr a
   lsr a            ; high nibble
   sta leds,x         ; this byte goes on the left
   inx
   inx
   rts      
   
   org $fffc		; +4
   dw start
   db VERSION,REVISION

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$0000-$7FFFF    RAM
$8000-$8007    LEDs
$8800          Keyboard
$9000-$900F    6522
$A000-A001    6850 UART
$B000          Alternate keyboard? Might simplify things
$C000-FFFF    EEPROM
$FF80-FFFF    DROM (when enabled)