ET-3400 ROM - Message Program Assembly

I intended to place this programming test in the new 8K ROM section of the ROM replacement board, however the program I was copying from (out of the ET-3400 Manual) was self-modifying and needed a rewrite so that it would run in ROM and use the RAM in the lower 512 bytes for variables.

After I got into it I thought it would be relatively easy, but I was assuming that the 6800 CPU programming was similar to 6502 CPU programming since the 6502 was modelled on the 6800. However it turns out that was a false assumption, and my programming experience on the 6800 wasn't up to speed.

The 6800 doesn't have indirect addressing mode and the program was self modifying so that it could do a sort-of indirect addressing. Also there were no opcodes to transfer the X register to the ACCA or ACCB register or the stack as far as I could tell.

It was going to take me a lot longer to learn enough basic 6800 code to get this done in time, so I reverted to editing and extending the program in it's original RAM location. The resulting output will be the same though.

This is the final assembler listing of the program with modifications incorporated:

-----------------------------------------------------------------------
mark@HAL-9000:~/Documents/ET3400$ crasm -o retro.hex retro.txt
Pass #1
Pass #2
Crasm 1.8:                                                   page  1
                         1  ; RetroChallenge 2021/10
                         2  ; assembler: crasm in Ubuntu 16.04LTS
                         3  ; target: ET-3400 Microprocessor Trainer
                         4  ; original code in ET-3400 manual - Sample4
                         5  ; modified by Mark C
                         6  ; date: 26 Oct 21
                         7  
                         8          CPU 6800        ;target CPU
                         9  
                        10          OUTPUT HEX      ;generate INTEL Hex file
                        11  
                        12          ILIST ON        ;show included files in 
                         listing
                        13  
                        14  ; SAMPLE   4
                        15  ; OUTPUTS SAME MESSAGE AS PROGRAM 3
                        16  ; IN TICKER TAPE FASHION
                        17  ; USES MONITOR SUB ROUTINES REDIS AND OUTSTR
                        18  
  0000                  19          * = $0000       ;assemble at $0000
                        20  
                        21          CODE
                        22          INCLUDE ET3400MON.TXT
                         1  ;Heathkit ET3400 built in monitor subroutines
                         2  
                         3  
                         4  
  FCBC                   5  REDIS = $FCBC           ;RESET DISPLAY
  FE52                   6  OUTSTR = $FE52          ;OUTPUT CHARACTER STRING
  00F0                   7  DIGADD = $00F0          ;LEFT DIGIT STORAGE
  FE3A                   8  OUTCH = $FE3A           ;OUTPUT SEGMENT
  FE28                   9  OUTHEX = $FE28          ;DISPLAY DIGIT AND MOVE 
                         CURSOR TO NEXT
  C16F                  10  DG6ADD = $C16F          ;LEFTMOST DIGIT
  C15F                  11  DG5ADD = $C15F
  C14F                  12  DG4ADD = $C14F
  C13F                  13  DG3ADD = $C13F
  C12F                  14  DG2ADD = $C12F
  C11F                  15  DG1ADD = $C11F          ;RIGHTMOST DIGIT
                        16  
                        17  
                        23  
0000 7F0007             24  START   CLR     MORE+1   ;CLEAR POINTER
0003 CE002C             25  NEXT    LDX     #MESSA   ;MESSAGE ADDRESS
0006 A600               26  MORE    LDAA    0,X      ;GET CHARACTER
0008 A745               27          STAA    OUT+3-MESSA,X  ;STORE CHAR. AT O
                                UT PLUS
000A 08                 28          INX              ;NEXT CHARACTER
000B 8C0032             29          CPX     #$32     ;FULL WORD YET?
000E 26F6               30          BNE     MORE
0010 8D13               31          BSR     HOLD     ;HOLD DISPLAY
0012 BDFCBC             32          JSR     REDIS    ;FIRST CHAR. TO LEFT DI
                          GIT
0015 BD006E             33          JSR     OUT
0018 B60007             34          LDAA    MORE+1   ;FIRST CHARACTER POINTE
                          R
001B 4C                 35          INCA             ;MOVE STRING UP ONE CHA
                          RACTER
001C B70007             36          STAA    MORE+1   ;NEW FIRST CHARACTER
001F 813C               37          CMPA    #$3C     ;LAST CHAR. TO LEFT DIG
                          IT YET?
0021 26E0               38          BNE     NEXT     ;BUILD NEXT WORD

Crasm 1.8:                                                   page  2
0023 20DB               39          BRA     START    ;DO AGAIN
0025 CE8000             40  HOLD    LDX     #$8000   ;TIME TO WAIT
0028 09                 41  WAIT    DEX
0029 26FD               42          BNE     WAIT     ;TIME OUT YET?
002B 39                 43          RTS
                        44  
002C 080808080808       45  MESSA   DB $08,$08,$08,$08,$08,$08      ;------
0032 056F0F051D00       46          DB $05,$6F,$0F,$05,$1D,$00      ;retro
0038 4E177D30306F       47          DB $4E,$17,$7D,$30,$30,$6F      ;Challe
003E 157B6F006D7E       48          DB $15,$7B,$6F,$00,$6D,$7E      ;nge 20
0044 6D3025307E00       49          DB $6D,$30,$25,$30,$7E,$00      ;21/10
004A 0000004F0F01       50          DB $00,$00,$00,$4F,$0F,$01      ;   et-
0050 79337E7E0000       51          DB $79,$33,$7E,$7E,$00,$00      ;3400
0056 051D15110005       52          DB $05,$1D,$15,$11,$00,$05      ;rom r
005C 6F67307D0D6F       53          DB $6F,$67,$30,$7D,$0D,$6F      ;eplace
0062 15116F150F00       54          DB $15,$11,$6F,$15,$0F,$00      ;ment
0068 080808080808       55          DB $08,$08,$08,$08,$08,$08      ;------
                        56  
006E BDFE52             57  OUT     JSR     OUTSTR   ;OUTPUT CHARACTER STRIN
                          G
                        58  ; OUTPUT STRING STORED HERE
0071 00000000000080     59          DB $00,$00,$00,$00,$00,$00,$80  ;char bu
                                         ffer and end char
0078 39                 60          RTS
                        61  
                        62          CODE
                        63  
                        64  
ERRORS:       0
WARNINGS:     0
Successful assembly...
 Last address       78 (120)
 Code length        f2 (242)
----------------------------------------------------------------------

The program simply scrolls a message on the 7-segment display. 

I ran the program and recorded a video which I will try and upload in my final blog entry next ...

Comments

  1. TonyOctober 31, 2022 at 7:42 AM

    Nice Article. Which Eprom programmer did you use to program chip?

    ReplyDelete
    Replies
    1. Rev 3ngOctober 31, 2022 at 7:54 AM

      Hi Tony, The Universal programmer I used to burn the AT28C64 EEPROM is a Wellon VP-299 that I picked up for a bargain on eBay. I believe the TL866 Plus will work too.

      Delete
    2. TonyNovember 1, 2022 at 12:01 PM

      Thanks

      Delete

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