Letters

Help Wanted

Dear Editor:

I have a special request. I would like to have some information on producers and shops which sell ZX81 music programs, like one which changes the ZX81 into an electric organ or a synthesizer. I own a ZX81 and I am very interested in making and playing music on it. Also I am interested in a good accounting system for a small business.

Arnar Matthiasson
[address omitted]
Borgarnes, Iceland

---

Dear Editor:

I recently acquired my ZX81 (16K) with little knowledge of programming under my belt. I received my first issue of SYNC (2:1), and I was excited at the prospect of using machine language. Then I encountered two problems:

1) I would be interested in knowing how to modify the “Flattop Lander” code for my machine. The system variables appear to be different, and I have no source equivalents.

2) I twice, no thrice, entered the “Life” program with no success. The initial border routine worked, but after I entered some numbers/cells the system would crash when I input 0 to continue. Are there any bugs? I even entered it once using Mr. Ornstein’s Window program (a long process I can assure you).

Any help you could give me would be appreciated. I enjoy your magazine, though I wish that it were monthly. Also, which back issues are still available?

Keith Liggeti
[address omitted]
Huntington Beach, CA

Ed.—The “Life” program did have some problems as some readers have called to our attention. The author has supplied the revisions which are included in our Glitchoidz Report. A few back issues of SYNC 1:2 are available at $2.50 each. Payment should accompany the order.

---

Dear Editor:

Enclosed is a list of several errors that I found in The Gateway Guide to the ZX81 and ZX80. I am sure that most readers would spot the errors quickly, but beginners may not. I feel that the book is well worth the money, as is The ZX81 Companion (but I wish more about the intricate working of the ROM had been included).

Now a question. Is there any way to write a machine language routine to read TRS-80 500 BAUD tapes? I sent for a kit to do so, but it is really designed for an S-100 Bus operating with a Z80 CPU. How about an article in SYNC on this? How about more articles on machine routines to extend the 8K Basic like the READ routine in Edward Kennedy’s article (SYNC 1:5). How about MERGE? How about a routine to set a single pixel?

I liked very much David Ornstein’s article on the 4K ROM SAVE command. I hope that he does as threatened and writes an article on a full fledged cassette based I/O processing system, especially if he includes details on wiring the cassette to forward or reverse under CPU control.

I have also sent for a light pen (designed for the TRS-80) that I would like to hook up to my 8K ROM ZX80. Any suggestions? How about some articles on adding output ports to make the ZX80 compatible with TRS-80 peripherals?

Timothy McIlwee
Flagler Palm Coast High
[address omitted]
Bunnell, FL

Ed.—The corrections have been passed on to our Book Division. Again our readers have set out a number of challenges. We look forward to your responses.

Program Problems

Dear Editor:

I am the owner of a ZX80 and a ZX81. I have been trying some of the examples in your magazine and have been having problems. E.g., In Robot Composer (1:5) I cannot enter line 150; in Defuse (1:5), lines 10, 20, 30, 40; in Graphic Surprises (1:3), lines 130, 200, 1010; Variable Conversions (1:3), line 30; The TL$ Function (1:4), line 50 LET P$=TL$(A$) (syntax error); Mini-Billboard, line 21 LET A$=TL$(A$). Please tell me how I can do these.

Edward A. Parker
[address omitted]
Altadena, CA

Ed.—First and foremost be sure that you are entering your program on the correct ROM. All the programs in issues 1:1, 1:2, 1:3, and 1:4 are for the 4K ROM and cannot be entered on the 8K ROM without translation. In issues from 1:5 on programs for both ROMs are included, and the machine requirements for the programs are given at the top of the page. Most of the lines referred to above seem to involve the random feature. On the 4K ROM RANDOMISE is on the J key and RND(x) must be spelled out; on the 8K ROM INT and RND are functions and must be entered directly from the keyboard in one keystroke. In the line P$=TL$(P$), ignore the syntax error and finish typing in the line. It serves to remind you that something must be completed, e.g., the second parenthesis or quotation marks. For the 8K ROM the line must be rewritten as LET P$=P$(2 TO #).

ZX80 Slow Mode

Dear Editor:

Is there any way that I can get my ZX80 with the 8K ROM to run in the SLOW mode?

Anthony Larry
[address omitted]
West Haven, CT

Ed.—At present the only method we have heard of is the MicroAce Video Upgrade Kit (see a review of this kit in SYNC 2:1, p. 27). However, MicroAce has closed down its U.S. operation, and we have received no information whether a U.S. distributor for the kit has been arranged. MicroAce can be reached at: MicroAce Compshop, 14 Station Road, New Barnet, Hertfordshire EN5 1QW, United Kingdom.

The Hidden Chessmen

Dear Editor:

I have received several requests to convert The Hidden Chessmen (SYNC 1:6) to use on a ZX81. Presently, I have an 8K ROM in my ZX80 and a 16K RAM pack. The following changes were needed to get the program running:

 1 LET B=1+INT(8*RND)
 2 LET C=1+INT(8*RND)
 3 LET K=1+INT(8*RND)
 4 LET L=1+INT(8*RND)
 6 LET R=1+INT(8*RND)
 7 LET S=1+INT(8*RND)
44 LET X=INT(Q/10)
50 LET Q=PEEK 16396+256*PEEK 16397+2*X-1+66*(Y-1)
62 IF . . . THEN POKE(Q+33),48
64 IF . . . THEN POKE(Q+34),55

The program takes more than 1K RAM, but I think it will fit in 2K.

Roger Haar
[address omitted]
Martin, OH

Ed.—Our thanks to Roger Haar for these changes to make the program available to our 8K ROM readers.