Sinclair ZX80 / ZX81 / Z88 Forums

Hi Again, yesterday i soak tested a ULA for over 3 hours and all is well it is been packed up now ready to wing its way over to you. the commodore monitors work fine but do need the link on the ula shorting as they have a high impedance input on that composite input. from the scope trace it does loo...

unless you really need the capacitor i'd ditch it... most modern tv's don't have any DC bias on the composite inputs.

regards Andy

Don't let Moggy know but try a heatsink on the ULA...

BTW which composite mod did you do?

Andy

Welcome, hope you find some useful information.

Regards Andy

Hi

is this keyboard available yet ?

regards Andy

Andy (a member here) has seriously overclocked a ZX81. However he was using his older ULA replacement module. With a standard Sinclair ULA, overclocking is difficult as you can’t change the frequency without messing up the screen display. Mark Slight correction, the older ULA could do 2X speed... m...

Paul wrote: ↑Mon Apr 01, 2019 6:23 am Hi Andy, I guess it would be possible internally as well?
Which bytes have to be changed?
Do you know how the channel 2/3 selection works? Maybe this could be (ab)used for ROM switching?
Kind regards Paul

Nice idea, worth looking into for sure.

lets assume we are going to use the whole 16K to store a single whole number dont want ony of the rounding loss business with floating piont numbers and exponents ( although the number you could store would be huge ) so we have 16384 * 8 bits to store our large integer (2^0 + 2^1 + 2^2 .... + 2^1310...

Not certain it can be done that way, least i never was able on my ts1500, however you can use and external rom and hardcode it for 50hz

regards Andy

McKlaud wrote: ↑Tue Mar 05, 2019 1:16 pm Dishwasher would be better

i had a commodore pet universal main board ( from a cbm 4032 machine) in the kitchen sink... my missus thought i'd gone nuts... works a treat and is clean to boot now