Sinclair ZX80 / ZX81 / Z88 Forums

indeed you can, remarkable as I have not seen them anywhere else, before or after I saw them on a ZX80, but be aware that they are also selling worthless plastic plugs used to keep IC's falling out of IC tubes as if they were these rivets, and they ask absurd prices for those too. Is anybody really ...

the thread about replacement cases is here: http://www.sinclairzxworld.com/viewtopic.php?f=7&t=752& I planned to create a case for my ZX81 clone out of laser-cut wood or plastic, I considered 3-D printing, but my case will be at least 16 cm wide, too much for most 3-D printers. For the vacuum molded...

@paul, yes a series resistor will prevent a large inrush current through the reset button, perhaps not really necessary, but a good idea, I will look to see if I have room for it, otherwise the resistor could be put on the keyboard PCB (with the reset buttons). @Buka, I don't know of any ZX80 clone ...

Well I found a .PDF to .PNG online converter, so I don't have to wait until tomorrow to convert the .PNG at work, so here it is:

Darn! :o you found another design error, obviously I intended U30 to be a latch, but copy/pasted the wrong chip. It should have been another 74HC574, I don't understand I didn't see that, must have overlooked it a hundred times. I'm very happy you found that, thanks! ;) as for audio during writing t...

Well, yes, the speaker output.. I decided I wanted the barest minimum I/O expansion to give my clone some general purpose I/O, so I created one 8-bit output latch. Initially I wanted only a simple clicker 1-bit audio output, and yes I realize that generating any sound beyond perhaps a simple key cli...

@pokemon, you asked about the turbo circuit, it actually based on wilf rigters bare bones turbo circuit http://www.user.dccnet.com/wrigter/index_files/turbo.htm at least the clock doubler part of it is. The turbo latch is controlled so that the turbo is turned automatically while the Z80 is "executi...

Looking what is available in single gate logic (preferably in a SOT23-5 package), and the cheapest device, I come out at the 74HC1G08 AND port, when using active low (/VSYNC and /HSYNC) inputs and and active low output /CSYNC Meaning, the output is low if either /VSYNC or /HSYNC is low. Will change ...

Yes, that is why I stated the problem with that is that the Hsync pulses are not in the right position, as the ZX81 does NOT produce an interlaced picture. But thanks for the detailed explanation. Main reason for making it possible to use an XOR was that I simply wanted to see what the effect is in ...

Well, yes, its the old logical rule that inverting both inputs and outputs turns an OR into and AND and vice-versa, I use that extensively in my designs. For example originally I had planned to use 4-input ANDs for the VSYNC and /PORCH, but I saw that most of the AND inputs were active LOW, and it w...