Sinclair ZX80 / ZX81 / Z88 Forums

Yes folks you heard it here first... Very much still a work in progress

using real 5v part nobody wants stinky 3.3v stuff

Shall we play a game? spot the difference....


Got it yet? On the left we have altera unobtanium, Whilst on the right Atmel still in production...but for how long who knows>

anyway the plan is to produce two versions, price will be cheaper for standard version because chip is cheaper

Enhanced version similar in operation to my old altera design and will include clock doubling also but of course will require those extra wires ( if you know, you know )

the form factor is unusual and may not be for everyone it will fit inside an original case but better use an old beat up one since it requires the removal of the pcb support pillar near the regulator.

Regards Andy

Hi Andy, great that you're making another Version!
Could you please post a picture with an Issue1 and an Issue3 board for mounting reference?
I can't really imagine how it fits inside
Cheers Paul

Yes folks you heard it here first...


Really?

Hi Paul,

the issue 1 photos are in a socket on the board and is operational, The issue 3 board still has a soldered in ula on it so i just placed the MK4 ula over it for the piurposes of taking a photograph.








@Moggy... the cats out of the bag now huh

Thanks, that looks good.
Would a replacement DC-DC converter (recom) instead of 7805 still fit?

i think so i measure the gap between pcb's at 9.5 mm when the MK4 is mounted in a turned pin socket. the 1A 5v recoms are 7.5mm thick, but you might have to make it's leads a little longer. so that it cann lay on its back.

regards

I think most of us lay the Recom/Traco types on their back anyway so no problem I would have thought.

Can't wait for them to be on sale though I may have to sell MY TS1500 to buy them!

I'm also looking forward to get my hands on the enhanced version

Exciting times!

Little update,

pretty much proved the device works as expected, missed a pull up resitior off, and a capacitor LOL.

i still plan to produce 2 versions, standard and enhanced

Standard version plug in and go. composite video 1v p-p into a 75 Ohm load ( most tv's and monitors)

Enhanced version will be approx. GBP 5 more expensive (different chip ) and will offer Clock doubling, inverse video, inverse border, M1not, and a constant 3.25Mhz output for people with zonx or other sound cards that need the clock. of course to use these features 5 extra wires need soldering to connect the address lines that are not present at the ULA socket.

Things that are different between this enhanced version and my really old altera design ( that had clock doubling ) .. The reset wire and resistor are gone. you can still lock the features set but resetting requires a) a power cycle. or b) exciting code at memory address 0. i.e an external system reset, causing the cpu to start exciting code at address - or a deliberate RAND USR 0 .

Clock doubling in FAST mode still requires a POKE 1001,x ( x doesn't matter) but you no longer need to set a feature bit to allow this.
Rompatch is also automatic, this allow easier switching back to slow mode from fast when in clock doubled mode.

so currently the control bits are as follows, we now have 2 spare bits.... what to do with them ???
finally i estimate ( and thius is a rough guess based on todays prices )
Standard ULA to cost 20 GBP + postage cost (currently GBP 8.75 to most of Europe)

Enhanced ULA to cost 25 GBP + postage cost (currently GBP 8.75 to most of Europe)







Those wires... (if ya know, ya know !)

regards Andy

P.s those faint diagonal lines seem to be a rolling shutter effect and you cant see them in real life )