Search found 42 matches

by sheddyian
Fri Jan 15, 2021 5:36 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

1024MAK wrote: Sun Jan 03, 2021 8:38 pm Why Wait - see this topic ;)

Mark
Thanks for this - I've just fitted it using a BC307 and a 10K resistor, and it's working nicely.

Frames count from CLKFREQ.p benchmark has dropped from 1879 to 1717 so it's definitely running faster.

Thanks

Ian
by sheddyian
Wed Jan 13, 2021 4:23 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

Thanks for the responses and suggestions. I've had some success at last, using the tapeutils program. I was running Peppermint Linux on this laptop, it's got 2GB RAM and dual core CPU so it's not the slowest of wheezy laptops, but it's not blistering either. I think it's about 15 years old. Anyway, ...
by sheddyian
Mon Jan 11, 2021 10:53 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

OK.. think I've found the fault. It is tape loading related.. but not levels. Just listened to the audio when playing the larger .p files via JAVA tapeutils program on the Linux laptop - and there's gaps in it. This wheezy laptop seems to be struggling to give continuous sound output for the larger ...
by sheddyian
Mon Jan 11, 2021 10:26 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

Here is a simple program to test a machine that has 16k bytes of RAM: 16k RAM test program using DIM Please note that when this is run, the screen will immediately go black/blank. It takes about one minute to run on a 50Hz ZX81. Mark Damn, I wanted that to fail to be consistent with my expectations...
by sheddyian
Mon Jan 11, 2021 10:25 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

Your results are correct for the normal 16k byte upgrade. Thanks for confirming that. I did once know a bit about the ZX81 memory layout, but that was a long time back! Maybe you should instead post up some photos showing the work on your board that you have done? I was almost too ashamed as it loo...
by sheddyian
Mon Jan 11, 2021 10:18 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

It could be that your ram works perfectly, but loading can be a difficult task. You might be lucky loading a short 1k program, but not when the program is bigger. It doesn't feel like a tape loading error as such, because 1K or 2K programs were (and still are) loading successfully. The 4K maze game...
by sheddyian
Mon Jan 11, 2021 1:26 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

Yesterday I fitted an internal 16K upgrade to ZX81 #3. I also moved the late revision ULA to this machine, where it gives a better picture than it did when fitted to ZX81 #1. No shadowing, no flickering, lovely crisp bright display from the UHF on a colour TV. To upgrade to 16K, I followed the Tynem...
by sheddyian
Mon Jan 11, 2021 12:50 pm
Forum: Hardware
Topic: Attic 81's - My collection and attempts to repair
Replies: 51
Views: 2225

Re: Attic 81's - My collection and attempts to repair

I have built this one - the MEEPROMMER . A shield for the Arduino. I used the gerber files and ordered some in china. They are just PCBs so you have to add the components yourself. I can one the for a few euros + shipping. Thank you, I will have a look at that. I am aware of Arduinos but don't have...
by sheddyian
Sun Jan 10, 2021 8:31 pm
Forum: Hardware
Topic: CLKFREQ.P benchmark on 2K ZX81
Replies: 12
Views: 322

Re: CLKFREQ.P benchmark on 2K ZX81

Just for completeness / in case anyone is interested, the results from running the above CLKFRQ2K.P program are : Machine Frames ======= ====== 2K ZX81 2237 2K Emulator 2216 16K ZX81 1879 16K Emulator 1868 ZX81 had either 2K or 16K available onboard, no other mods, late revision ULA. Emulator is Eig...
by sheddyian
Sun Jan 10, 2021 8:24 pm
Forum: Hardware
Topic: CLKFREQ.P benchmark on 2K ZX81
Replies: 12
Views: 322

Re: CLKFREQ.P benchmark on 2K ZX81

[...] [*]The amount of available RAM affects the speed of BASIC. If there is less than about 4K bytes of RAM, the screen area operates in collapsed mode to reduce the amount of RAM that is needed. Taken to the extreme, the display file can be only a handful of bytes. As the program runs, every time...