serial_echo.s

  
; jsio.asm jha 8/2/2018 testing sio
; https://wiki.theretrowagon.com/wiki/Imsai_8080
; Originally from a Monitor program code by John Garza hence the EQUates
; http://jgarza.sdf.org/files/M72.ASM
;
; Important init code from VCF forums
; handy VCF threads for configuration
; http://www.vcfed.org/forum/showthread.php?64964-Imsai-FIF-FDC-project
; http://www.vcfed.org/forum/showthread.php?37137-How-to-get-output-from-SIO-with-Intel-8251A-USART
; 
; uses a straight through cable.

;------------------
;IMSAI 8080 EQUATES

LEDS	equ	0FFh	;IMSAI front panel output LEDs (top left)
SWCH	equ	0FFh	;IMSAI front panel input switches (left)

; channel a
TTS     equ     03h     ;SIO channel A command port
TTI     equ     02h     ;SIO channel A data port (yes input=output)
TTO     equ     02h     ;SIO channel A data port

; channel b
; TTS     equ     05h     ;SIO channel B command port
; TTI     equ     04h     ;SIO channel B data port (yes input=output)
; TTO     equ     04h     ;SIO channel B data port

TTYDA   equ     02h     ;tty data available (ready to receive?) 
TTYTR   equ     01h     ;tty terminal ready (ready to transmit?)

    org 0000h
init:
    mvi a,0    
    out TTS
    out TTS
    out TTS
    mvi a,040h
    out TTS
    ; mvi a,04eh  ; 8,1,n
    mvi a, 7eh
    out TTS
    mvi a,037h
    out TTS

inout:               ; loop read from serial, write it to serial. Serial terminal echo.
    in TTS
    ani TTYDA        ; DATA available?
    jz inout
io1:
    in TTS
ani TTYTR           ; ready to receive?
    jz io1
    in TTO          ; read character
    out TTO         ; write
    jmp inout       ; repeat
    end