---
title: "2068 Code Bytes #3"
type: "article"
slug: "2068-code-bytes-3"
url: "http://localhost/article/2068-code-bytes-3/"
markdown_url: "http://localhost/article/2068-code-bytes-3.md"
published_at: "2026-03-12T18:29:47+00:00"
modified_at: "2026-07-25T23:12:33+00:00"
featured_image:
  url: "http://localhost/wp-content/uploads/2022/04/20230809-041332.jpg"
excerpt: "Third installment in a series on interrupt-driven Z80 machine language programming for the Timex/Sinclair 2068. Covers a BLINK routine that alternates two User Defined Graphics characters on screen using variables for timing, position, and attributes, followed by three sound-effects routines: a border-toggle BEEP, a gun/bomb effect, and a whistle-and-bang bomb effect. Full machine code listings…"
category:
  - name: "SMUG Bytes"
    slug: "smug-bytes"
    taxonomy: "category"
    url: "http://localhost/category/periodicals/smug-bytes/"
post_tag:
  - name: "Best of Timex/Sinclair 2068 Articles and Documents"
    slug: "ts2068best"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts2068best/"
  - name: "Machine language programming"
    slug: "machine-language"
    taxonomy: "post_tag"
    url: "http://localhost/tag/machine-language/"
  - name: "TS 2068"
    slug: "ts2068"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts2068/"
  - name: "Type-in program"
    slug: "type-in-program"
    taxonomy: "post_tag"
    url: "http://localhost/tag/type-in-program/"
model:
  - name: "Timex/Sinclair 2068"
    slug: "ts-2068"
    taxonomy: "model"
    url: "http://localhost/model/ts-2068/"
indiv:
  - name: "Lloyd Dreger"
    slug: "lloyd-dreger"
    taxonomy: "indiv"
    url: "http://localhost/indiv/lloyd-dreger/"
publication_r:
  id: 37935
  title: "SMUG Bytes"
  type: "periodical"
  url: "http://localhost/periodical/smug-bytes/"
authors_r:
  - name: "Lloyd Dreger"
    slug: "lloyd-dreger"
    taxonomy: "indiv"
    url: "http://localhost/indiv/lloyd-dreger/"
volume: "10"
issue: "3"
issues_articles:
  - id: 50215
    title: "SMUG Bytes v10 n3"
    type: "issue"
    url: "http://localhost/issue/smug-bytes-v10-n3/"
pages: "3"
pubdate: "June 1993"
related_articles:
  - id: 64994
    title: "2068 Code Bytes #5"
    type: "article"
    url: "http://localhost/article/2068-code-bytes-5/"
  - id: 64996
    title: "2068 Code Bytes #6"
    type: "article"
    url: "http://localhost/article/2068-code-bytes-6/"
  - id: 64998
    title: "2068 Code Bytes #7"
    type: "article"
    url: "http://localhost/article/2068-code-bytes-7/"
  - id: 64991
    title: "2068 Code Bytes #4"
    type: "article"
    url: "http://localhost/article/2068-code-bytes-4/"
archive_link: false
---

Third installment in a series on interrupt-driven Z80 machine language programming for the Timex/Sinclair 2068. Covers a BLINK routine that alternates two User Defined Graphics characters on screen using variables for timing, position, and attributes, followed by three sound-effects routines: a border-toggle BEEP, a gun/bomb effect, and a whistle-and-bang bomb effect. Full machine code listings with addresses and mnemonics are provided throughout.

***

We continue our discussion of interrupt driven routines with BLINK which alternates two different User Defined Graphic characters to the screen.

We need a few more variables, namely:

- TIME–to count down the 1/60th of seconds before the next change.
- WHICH–Character 1 or 2 presently on screen.
- CHAR1–Which UDG number (from o to 20, not the Basic #).
- ATTR1–Attribute of ink/paper for characterl.
- CHAR2–ZND UDG charcter #.
- ATTR2–2ND attribute.
- POSY and POSX–BASIC Type AT 0 to 20 and 0 to 31.
- ATTRA–Address of attribute…

We enter these at the start of the program together with the variables for the music program and put the Blink part in front of the Tune part which we did in our first 2 parts. We again have a new ORG and DISP which will leave our assembled code at 28000.

The interrupt routine continues with the music which we discussed in previous installments. Remember to change your jump address at 65022. You also have to write a routine to enter all the Blink variables.

There are other ways of creating sounds without using the sound generator. One of these is the toggle of the border output–register 294. This is used in Beep. It is such a short routine it fits almost anywhere you want to put it and so is given without addresses.

War games require good shooting and bomb effects. In this routine the whistle and the bang produce a bomb effect. Just doing the bang is a good gun effect by itself.

The game uses a saved variable called EFFECT to toggle on and off the bomb or gun sounds. Again, the routine can go anywhere so we give it without addresses–the XXX being dependent upon where it is assembled.

This completes the sound and interrupt driven programs. Next time we will give you a general menu routine, one that can be used on any size up to a full screen with a cursur that jumps from top to bottom automatically.

ORGEQU 64817

DISPEQU 28714

TVFLAGEQU 23612

6481720TIME1DEFB 20

648181WHICHDEFB 1

648190CHAR1DEFB 0

648200ATTR1DEFB 0

648210CHAR2DEFB 0

648220ATTR2DEFB 0

648230POSYDEFB 0

648240POSXDEFB 0

648250,0ATTRADEFW 0,0

And Previously:

648271SOUNDFDEFB 1

648281TUNEDEFB 1

648290FINEDEFB 0

648300COARSEDEFB 0

648310TIMEDEFB 0

648320,0NEXTDEFW 0,0

We call this address:

64834245BLINKPUSH AF

64835229PUSH HL

64836197PUSH BC

64837213PUSH DE

648388EX AF,AF’

64839217EXX

64840245PUSH AF

64841229PUSH HL

64842197PUSH BC

64843213PUSH DE

WE HAVE SAVED ALL VARIABLES NOW FORCE USE OF TOP SCREEN

6484458,60,92LD A,(TVFLAG)

64847245PUSH AF

64848203,135RES 0,A

6485050,60,92LD (TVFLAG),A

6485333,49,253LD HL,TIME1

6485653DEC (HL)

IF NOT ZERO NOT YET TIME TO CHANGE

6485732,46JR NZ,PLAY

RESET THE BLINK CLOCK

6485954,20LD (HL),20

6486135INC HLTO WHICH

6486262,2LD A,2

64864190CP (HL)

IS WHICH =2ND CHAR?

6486532,3JR NZ,BK1

6486753DEC (HL)SET TO 1

6486824,3JR BK2

6487052BK1INC (HL)SET TO 2

6487135INC HL–CHAR1

6487235INC HL–ATTR1

6487335BK2INC HL–CHAR2/CHAR1

64874126LD A,(HL)

64875254,0CP 0— IF TRUE, BLINK NOT BEING USED

6487740,26JR Z,PLAY

64879229PUSH HL

64880245PUSH AF

USE POSX AND POSY TO DO AN AT

6488162,22LD A,22

64883215RST 16

6488458,56,253LD A,(POSX)

64887215RST 16

6488858,55,253LD A,(POSY)

64891215RST 16

64892241POP AF

64893230,15AND 15

64895198,144ADD A,144

A is now the Basic UDG character #

64897215RST 16

64898225POP HL

6489935INC HL–TO ATTR

64900126LD A,(HL)

6490142,57,253LD HL,(ATTRA)

64904119LD (HL),A

64905241PLAYPOP AF

6490650,60,92LD (TVFLAG),A

243BEEPDI

175XOR A

1,254,0LD BC,254

22,0LD D,0

203,231BOSET 4,A

237,121OUT (C),A

16,254B1DJNZ B1

203,167RES 4,A

237,121OUT (C),A

16,254B2DJNZ B2first byte obscured by scan blob; reconstructed from DJNZ opcode

21DEC D

32,241JR NZ,BO

251EI

201RET

58,0,0GUNLD A,(EFFECT)printed 58,xxx,xxx

254,0CP 0

200RET Z

197PUSH BC

FIRST STOP THE MUSIC

205,53,255CALL 65333(STOP)

[*unreadable*] ONLY THE BOMB

33,110,0EXPLD HL,LIST+11printed [*unreadable*],XXX,XXX — opcode reconstructed as 33

6,8LD B,8

205,91,0EOCALL INOUT2printed 205,XXX,XXX

16,251DJNZ EO

6,120LD B,120

118EX1HALT

16,253DJNZ EX1

6,4LD B,4

205,91,0BWCALL INOUT2printed 205,XXX,XXX

16,251DJNZ BW

DONE, NOW RESTART MUSIC

205,1,255CALL 65281(SETUP)

193POP BC

201RET

58,0,0BOMBLD A,(EFFECT)printed 58,XXX,XXX

254,0CP 0

200RET Z

197PUSH BC

TURN OFF MUSIC

205,53,255CALL 65333(STOP)

62,15LOOPLD A,15

33,99,0LD HL,LISTprinted 33,XXX,XXX

6,2LD B,2

205,82,0BXCALL INOUT1printed 205,XXX,XXX

16,251DJNZ BX

245PUSH AF

126LD A,(HL)

35INC HL

211,245OUT (245),A

241POP AF

60INC A

254,141CP 141

IF DONE JUMP TO GUN

40,197JR Z,EXP

245PUSH AF

211,246OUT (246),A

6,4LD B,4

205,91,0B4CALL INOUT2printed 205,XXX,XXX

241POP AF

118HALT

24,221JR LOOP

245INOUT1PUSH AF

126LD A,(HL)

35INC HL

211,245OUT (245),A

241POP AF

211,246XOUT (246),A

201RET

126INOUT2LD A,(HL)

35INC HL

211,245OUT (245),A

126LD A,(HL)

35INC HL

24,245JR X

0,4,2,7,56,8,15,9,15LISTDEFB 0,4,2,7,56,8,15,9,15

10,15,0,1,6,6,7,7,8,16,9DEFB 10,15,0,1,6,6,7,7,8,16,9

16,10,16,12,56,13,8,9,0DEFB 16,10,16,12,56,13,8,9,0

10,0,12,0,13,0DEFB 10,0,12,0,13,0

***

#### About this transcription

This listing was transcribed from the original scan and checked line by line. The published address column, object-byte column and mnemonics each independently determine the program, so all three were cross-referenced against one another: 65 lines carried both bytes and mnemonics and were fully verified, and a further 66 lines printed without an address column had their object bytes and relative jumps checked.

The bytes are authoritative where they disagree with the printed mnemonics. 3 such discrepancies were found:

- **64825**, printed as `DEFW 0,0`, should read `DEFW 0` — the next line is at 64827, so this reserves one word, not two; assembling the printed form pushes everything after it four bytes out of place
- **64832**, printed as `DEFW 0,0`, should read `DEFW 0` — the next line is at 64834, so this reserves one word, not two
- **GUN+68**, printed as `JR Z,EXP`, should read `40,196` — as printed, the displacement targets one byte past EXP, landing inside the LD HL,LIST+11 instruction; 196 targets EXP exactly and reconciles the block

2 symbols and jump targets referenced here are defined outside the published excerpt and could not be verified.