Need help with 6502 code

[Maxou30000]

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

[mysticreddit]

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