Epson HX-20 Terminal Program

To be able to convert the Epson HX-20 into to a terminal using its RS-232C port, I made this assembly program which can be assembled with dasm:

        processor hd6303

; Kernel routines:
DSPSCR  equ $FF4F
RSMST   equ $FF88
RSONOF  equ $FF85
RSOPEN  equ $FF82
RSGET   equ $FF79
RSPUT   equ $FF76
RSCLOS  equ $FF7F
KEYIN   equ $FF9A
KEYSTS  equ $FF9D
MENU    equ $FF25
SCRFNC  equ $FF5E

; Kernel variables:
RSDCNT  equ $01C2

        org $1000 ; Run from HX-20 RAM.
; Program:
start
        ; Set virtual screen size.
        ldx #packet
        jsr SCRFNC
        jmp endpack
packet
        dc.b $87   ; Screen size function
        dc.b 19    ; Columns
        dc.b 3     ; Rows
        dc.w $1300 ; Buffer address
endpack

        ; Clear the virtual screen.
        ldaa #$0C
        jsr DSPSCR

        ; Set RS-232 parameters.
        ldaa #%11110101 ; No parity, 1 stop bit, flow control off.
        ;ldab #%01001000 ; 1200bps, 8 data bits.
        ldab #%00101000 ; 300bps, 8 data bits.
        jsr RSMST

        ; Turn on RS-232.
        ldaa #1
        jsr RSONOF

        ; Setup RS-232 buffer.
        ldd #200
        ldx #$1100
        jsr RSOPEN

rschk
        ; Get one character from RS-232.
        ldd RSDCNT
        beq keychk
        jsr RSGET

        ; Output on virtual screen.
        jsr DSPSCR

keychk
        ; Check for keyboard activity.
        jsr KEYSTS
        beq rschk
        jsr KEYIN

        ; Terminate on 'ESC' press.
        cmpa #$1B
        beq end

        ; Check for swap between lowercase and uppercase.
        cmpa #$41 ; 'A'
        blt cdone
        cmpa #$5A ; 'Z'
        ble cutol
        cmpa #$61 ; 'a'
        blt cdone
        cmpa #$7A ; 'z'
        bgt cdone

        ; Covert from lowercase to uppercase.
        anda #%11011111
        jsr cdone

cutol
        ; Covert from uppercase to lowercase.
        oraa #%00100000

cdone
        ; Put one character on RS-232.
        jsr RSPUT
        jmp rschk

end
        ; Shut down RS-232.
        jsr RSCLOS
        ldaa #0
        jsr RSONOF

        ; Go back to main menu.
        jmp MENU

It is only a "dumb" terminal supporting a few of the basic ASCII control codes, which happens to be handled automatically by the "virtual screen" routines in the HX-20 ROM code. It's best to run the communication at 300 baud, which is hard-coded into this program. Running faster baudrates will cause the receive buffer to overflow because writing to the LCD screen and scrolling it is too slow.

For convenience, here is a BASIC representation of the program:

1 DATA 206,16,9,189,255,94,126,16,14,135,19,3,19,0,134,12
2 DATA 189,255,79,134,245,198,40,189,255,136,134,1,189,255,133,204
3 DATA 0,200,206,17,0,189,255,130,252,1,194,39,6,189,255,121
4 DATA 189,255,79,189,255,157,39,240,189,255,154,129,27,39,29,129
5 DATA 65,45,19,129,90,47,13,129,97,45,11,129,122,46,7,132
6 DATA 223,189,16,86,138,32,189,255,118,126,16,40,189,255,127,134
7 DATA 0,189,255,133,126,255,37
8 FOR I=4096 TO 4198
9 READ A
10 POKE I,A
11 NEXT I
12 EXEC 4096

Before loading this BASIC program, the "MEMSET 8192" BASIC command must be run to move the program area, to avoid corrupting anything.

Here is a YouTube demo video of the terminal program in action against a Linux host to do some rudimentary web browsing.

Topic: Scripts and Code, by Kjetil @ 10/11-2023, Article Link