TWO QUESTIONS
Can you answer these questions for me please?
(1) What is the largest number the ZX81 stores as an integer?
(2) I would like to use my ZX81 as a remote terminal to connect with a mainframe but the mainframe requires a @ before all system commands and the ZX81 does not have a @. Is there any way around this problem?
Ronny Richardson
Chamblee, Georgia
The ZX81 stores integers as eight significant figures (four bytes) and a one byte exponent + 38, ie. 9999999 or 9.9999999 + 38.
About the @ — it is 4OH ASCII which is 64 in the decimal system. All your data would have to be converted into ASCII since this is the language most mainframes use. A short machine code program could do this. You could do it in BASIC but it would be very slow. In your machine code program you would redefine the keyboard and then establish a link with the mainframe by developing a new set of control characters. If you need some more information, just write to us again. Good luck with your link!
COMPATIBILITY
Will the solid-state mini-cartridges and interface for the T/S1500 be compatible with the T/S1000?
Also, what exactly is a microdrive? And is it compatible with the T/S1000?
Terry Marshall
Kansas City, Missouri
The mini-cartridges will not plug into the T/S1000. However, if you save the software from the cartridge to a tape, the program will work. Also, all software for the T/S1000 will be compatible with the T/S1500 since the T/S1500 accepts both tape and cartridges.
A microdrive is a small disk drive which speeds up the loading and saving of programs as well as increasing reliability. You should check with the manufacturer regarding its compatibility with the T/S1000.
REMARKABLE
How do I save specific bytes of memory?
John Schmitt
Aylmer, Ontario, Canada
The best way to save machine language is to store it in a REM statement at the beginning of a program. For example, if your routine is ten bytes long, make your first statement:
1 REM XXXXXXXXXXThe ten Xs will reserve ten bytes starting at address 16516. Now poke your machine language into these ten bytes. The Xs will change to different characters.
You can now save your routine and run it with RAND USR 16516 statement.
DIFFICULT SAVES
I have a difficult problem that possibly can’t be solved on the T/S1000, ZX81. I need to save a particular block of memory on tape, to be loaded for future reference or use. (Example: Save locations 22500 to 27600; locations contain elements of one or more strings.) On other large units, there are commands which save it, but how can I do this on my ZX81?
Steven Bottoms
Lampoc, California
The save always starts at the beginning of the BASIC area.There is no easy way to save a particular block of memory unless the block starts at the beginning of BASIC. Some special pieces of software have been developed to help with this problem.
TECHNICAL NOTE
Regarding your In-Depth article of issue No. 1, “Inside the T/S1000, ZX81,” it is worth mentioning that the photo on page 43 is not necessarily what a T/S1000, ZX81 owner will find upon opening up his or her computer. The ZX81 is a five chip board with RAM locations 4a and 4b, so there will be two smaller chips at the right, and the CPU is nearest to them, followed by the ROM and then the ULA. Purchasers of the T/S1000 at $99 received the next step, which is a ZX81 board with the two RAM area ICs removed and the 2016 static chip (2K RAM) replacing them. More importantly, the $99 board is socketed, so all chips are therefore easily removable (using an IC puller/replacer) for troubleshooting and replacement, while the newer and cheaper version in the photo mentioned has soldered-in-place ICs which cannot be readily serviced. Maybe Timex will offer a CPU card for this purpose? Otherwise the new board is much neater in layout and more professional in appearance than the older ZX81 boards.
Also, an Atari or Atari-compatible joystick may be attached for those games where locating the key while watching the screen tends to take away from the fun. Several options are available, all cheap and fairly easy to perform.
For the sake of being neat I chose to install a plug for the joystick. The connection could be made direct if so desired, however. If direct, cut the plug end off the joystick cable and use the color codes. If a plug is installed, refer to the numbers embossed on the plug or to the diagram. To use keys 5-6-7-8 as up-down-right-left is not possible with this method, however 6-7-8-9-0 is; and turns out to be a good alternative. 6, 7 and 8 are used for the same directions as indicated by the arrows on the keyboard; 9 is substituted for 5; and 0 is used for fire control.
Connections to Sinclair KB ports:
DE9P No. Color Keyboard
Code connector
8 Black 8
2 Blue 1
1 White 2
4 Brown 3
3 Green 4
6 Orange 5
Using the joystick has the same result as if the related key were depressed; so the software requires writing for keys “6”, “7”, “8”, “9”, “0”. As an example, in the Laser Cannon listing in issue Number 2, change line 130 from IF INKEY$=”8″ to IF INKEY$=”0″… and line 140 from IF INKEY$>”5″… to IF INKEY$>=”0″… and line 190 change “8” to “0”. This enables key 0 as fire control so movement and fire is the same as an Atari (control). The drawback is that machine code programs such as Flight Simulator are not as easily changed (it requires substituting the 9 key for the 5 key in machine code instructions).
The DE9P costs under $2 and the Atari joysticks range from $7 to $25 dependent upon manufacture and model. I used the controller that came with my VCS (2600) and it works just fine.
Ed Pardo
Hopatcong, N.J.
TAPE RECORDER BLUES
I will be more than happy to subscribe to your magazine if you can find a tape recorder that will LOAD. If you can get me a tape player that is guaranteed to work, I will even buy it from you.
Carlin S. Champlin
Brockport, Pennsylvania
Carlin, we’re both in luck. We get you to subscribe and you get to use a reliable tape recorder. While we make no guarantees, our programmers use the Sears ALC/SLIM cassette, the Realistic CTR 80, the General Electric 3-515/B, and say all work extremely well. So get a tape recorder and fill in the subscription form.
INVERSE VIDEO CHARACTERS
I just bought the first copy of your magazine and am very impressed. The many different departments with good articles and ideas are appreciated. I have only one suggestion so far. When printing programs, please include in the text what the inverse video characters are. At times it is difficult to determine what they are.
James A. Kosinski
Pittsburgh, Pennsylvania
Thanks for the suggestion, James. In previous program printouts, we have frequently represented graphic characters in words. In some cases this has confused people. For example, in 16 Pin Bowling (issue #2), we represented a graphic symbol as Graphic 1.
We should have described this as graphic shift 1 to produce the graphic character on the 1 key. This method was also used in Lemonade in issue #1.
ZX QUERY
Before I subscribe to Timex Sinclair User, I need to know how useful it will be to me, as I have a ZX81, not a T/S1000.
Kenneth H. Ahrendts
Mingo Junction, Ohio
Good point, Kenneth! The ZX81 and T/S1000 are virtually the same machine. The only difference between them is that the ZX81 has 1K RAM while the T/S1000 has 2K. Everything we publish for the T/S1000 will work with the ZX81 (keeping the 1K difference in RAM in mind). As well, anything written for the T/S1500 will work with the ZX81 and T/S1000 if they have 16K RAM. So don’t hesitate to subscribe now!
O CANADA
Congratulations on Timex Sinclair User. I have picked up Issue #3 and I shall certainly be subscribing.
Two points: Do you have the address for Timex Canada, and is there a Timex Users Group in Winnipeg or any other Canadian city?
Peter Winter
Winnipeg, Canada
Great to have you as a subscriber, Peter. You join a huge number of Canadians who receive Timex Sinclair User.
To answer your questions: TMX Canada Inc. is located at 635 Hood Road, Markham, Ontario L3R 4N6, and yes, there are Timex Sinclair groups in Canada. We do not have the address of any in Winnipeg but we’re sure one of our readers will send the information to us. There is a central club called Timex Canada Computer Club which can be reached through the TMX address.
CREDIT WHERE CREDIT IS DUE
Our apologies to Fred Blechman and Bill Payne, whose respective bylines were inadvertently omitted from the “Binary Banner” and “Setting FORTH” articles in Issue 4.
Write to us
Timex Sinclair User welcomes reader’s comments, compliments, queries and complaints. Letters should be addressed to: The Editor, Timex Sinclair User, 49 La Salle Avenue, Buffalo, N.Y. 14214. Please include your full name and address when writing.