Chess Clock by Sinclair review

David G · Post by **David G** » Wed Dec 11, 2024 5:50 am

Has anyone used this Chess Clock?

Apparently this was first published in 1981 by Mikro-Gen and by PSION, long before PSION started selling their famous personal organizers. Then Sinclair itself put out their own edition

Who wrote it? Unknown

All versions of Chess Clock are the same and came bundled with Chess, the 16K version. Chess Clock itself runs in 2K

It is a solid, functional utility, implemented in machine language. Here are my comments

Implements the features of a basic Chess clock. It is limited to 9 hours, 59 minutes and 59 seconds, after which it rolls around to 0.00.00 and keeps going

CHESS-CLOCK Auto-loads. Machine code is in a Variable, so if you jailbreak it, do not RUN, instead GOTO 1 (RUN will clear the variable and all the machine code)

Display addresses are hard-coded, so don't attempt to add any BASIC lines to the program, which will move the display up in memory resulting in a scrambled screen, and also because the machine code is above that, an out-of-control execution

machine code is straightforward, using a lot of variables and the full display. Because it was bundled with 16K Chess, it could count on plenty of memory, therefore there was no need to keep the program size compact. For example, it uses unpacked BCD but doesn't store it on the screen like most games, but in memory and after updating the numbers, then copies it to the screen. I wonder if the Clock was a port from another computing system?

Did they expect you to have two ZX81s? The CHESS-CLOCK program isn't integrated with the CHESS program (they are on opposite sides of the tape. I guess it was just a nice addition to the Chess tape and allowed you to track time when playing with physical game board

Because the ZX81 uses software-based TV display timing, programs can generate a precise sub-second clock signal by monitoring the System Variable FRAMES. Which this program does to good effect

Timing is wayayy off for the USA ZX81 and the Timex/Sinclair TS1000, which both run at 60hz

Now the last point is to be expected from the UK editions, but in 1982, Timex Computer Corporation itself put out a version of this tape. And it still used the 50hz timing. So, the clock runs too fast: after 1 minute, it displays 0.01.12

To work around this timing issue on 60hz machines, load the program bypassing autorun:

Code: Select all

FAST
RAND USR 836

Then change the timing:

Code: Select all

POKE 17654, 60
POKE 17659, 60

Finally, start the program:

Code: Select all

GOTO 1