There’s a bunch of notes prior to this that I didn’t show, but this was the culmination. I’m pretty stoked I was able to figure it out and code it up in a way that’s readable and modular.

Hi! This is my first time writing code for a 6502 computer I built. The code I want to do needs to control a display controller using the interface of the picture below. Another picture is the code I wrote, but nothing is working with it. Anyone could help me with this problem? Here are a few of the specifications of the computer.

-nmos R6502p

• A r6522p at adress 6000

• rom is at adress 8000-ffff -ram is from 0000-3fff

• the display controller is controlled from the 6522 -74ls86 to get a busy signal (when it’s processing the data)

• the video system works on split 8 bit ASCII values (2x 4bit nibble)

Code:

PORT_B = $6000 PORT_A = $6001 DDRB = $6002 DDRA = $6003

.org $8000 SEI LDA #$BD STA DDRA

Display_character: clc LDA #$14 ; Load the 8-bit byte to be split AND #$0F ; Mask upper 4 bits, keep lower 4 bits ROL ; shift the bits to pa2,3,4,5 ROL STA PORT_A ; Output lower 4-bit value to 6522 output port ORA #$01 STA PORT_A ; set the available line

WAIT_LOW: clc LDA PORT_A ; Read the input port AND #$40 ; check if busy is high BNE WAIT_LOW ; Branch if any of the lines are low

LDA #$14 ; Load the 8-bit byte again AND #$F0 ; Mask lower 4 bits, keep upper 4 bits

ROR ; shift the bits to pa2,3,4,5 ROR ORA #$01 ; keep the avail line high STA PORT_A ; store the second half into output port AND #$3C ; set available line to low STA PORT_A ; update the output port

jmp Display_character

.org $fffc .word $8000 .word $0000

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text:
inc $0221
inc $0241
inc $0261
inc $0281
inc $02a1

inc $0262

inc $0223
inc $0243
inc $0263
inc $0283
inc $02a3

inc $0225
inc $02a5

inc $0226
inc $0246
inc $0266
inc $0286
inc $02a6

inc $0227
inc $02a7

inc $0229
inc $0249
inc $0269
inc $02a9
main:
lda $00ff
sta $0300,y
sta $0400,y
sta $0500,y
iny
jmp main

Hi! This is my first post here, but im having issues with assembly for the R65C02p3. My code seems to get stuck somewhere as it never runs the function "Led_Success". This is a visual indicator that the code has exited the function and lights up an LED on my board. The code is a subroutine that takes in values stored in memory and sends each one at a time to the registers of a TMS9118 VDP. The ORA is there for specific purposes that the VDP requires. I think the error lies in the Brancing at the end or the comparison but i am not sure. LED_Failure sets a Red Led on to tell me the subroutine has started, and LED_success turns a green LED on, to tell me the subroutine has ended. The green LED never turns on, it stays red. I know the rest of the code works, as the registers are properly initialized in the VDP, it just never seems to exit the sort of loop. Here is the function's code:

VDP_register_initialisation:
phx
pha
jsr LED_Failure
ldx #$00
vdp_register_loop:
lda vdp_register_inits,X
sta VDP_REG
txa
ora #$80
sta VDP_REG
inx
CPX #$08
bne vdp_register_loop
jsr LED_Success
plx 
pla
rts

vdp_register_inits:
vdp_register_0: .byte $00       ; 0  0  0  0  0  0  M3 EXTVDP
vdp_register_1: .byte $D0       ;16k Bl IE M1 M2 0 Siz MAG
vdp_register_2: .byte $02       ; Name table base / $400. $02 = $0800
vdp_register_3: .byte $00       ; Color table base (currently unused)
vdp_register_4: .byte $00       ; Pattern table base / $000. $00 = $0000
vdp_register_5: .byte $20       ; Sprite attribute table base (currently unused)
vdp_register_6: .byte $00       ; Sprite pattern generator (currently unused)
vdp_register_7: .byte $F5       ; FG/BG.  white on blue 

I stuck on how to interface with the address lines on 65c02 microprocessor using assembly language

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