What does it exactly mean? Brand new Z80 MPUs and the support chips for it that were still available will no longer be manufactured. Yes, there are plenty of used Z80 MPUs on the grey market. But as with many things on the grey market (including trading sites like eBay) what you actually get may no...
In total there are 292 users online :: 12 registered, 0 hidden and 280 guests (based on users active over the past 15 minutes)
Most users ever online was 1411 on Tue 19th Mar 2024 09:18
Okay, that's weird... The keyboard matrix is pure hardware and what program is running shouldn't make any difference to the hardware. Having said that, BASIC and some games will ignore a key if two of the normal keys are detected to be pressed simultaneously. That may explain why the symptoms are di...
So, over the lifetime of the Spectrum, there were various changes to the circuitry including that of the DC-DC converter section. The website/blog you linked to is mine BTW. On your board, you may have either an earlier version or it has just been implemented differently. The service technicians tha...
It may be that the problems with the keyboard existed before you opened the case. Were you able to test it before opening it? The keyboard uses a membrane, which itself is wired as a matrix of "switches". The "normal" keys (those that are the same as in a rubber key model) use a ...
So, just the few instructions needed to switch banks then I guess? I was expecting a bigger speed penalty to bank switching. The latch chip that stores the extra address bits for the memory is just as quick as the Z80. The limiting factors are what you have to do in your software routine and the OU...
I assume you were using an original Sinclair power supply unit (model UK1400 9V 1.4A). This is not a universal mains voltage type, as it requires a nominal 240V AC 50Hz mains input voltage. It will not produce enough output voltage if connected to a 110V – 120V 60Hz mains supply. The good news is th...
Yes, it has definitely been modified. The (phono) output connector on the modulator (what was the UHF TV output) will now output a composite video signal. I can't tell which version (there are more than four...) of the composite video modification has been done. If you want to know, you need to care...
Oh, and during the RAM check that the ROM does, it may be possible to check for some RAM faults that the ROM code does not test for. It's not possible to pick up all RAM faults, because the intention of the ROM routine is to simply work out how much RAM is fitted, NOT if it works correctly. Hence th...
Nice 8-) The next step would be an instruction trace, Often knowing at what point the Z80 is no longer executing the expected sequence can help identify the problem, or at least narrow it down. If there is no input from the user, the machine should make it to the "copyright" screen with th...
It's called bank switching or paging, but at the hardware level, the value on the data bus from the OUT is stored in a latch (register). Then some of the bits are used as extra address lines to the memory (ROM and RAM). The effect of this is that as described above, the Z80 can only see a "wind...
CP/M became a big thing and certainly helped make the Z80 successful. I don't know if during the design of the Z80 CP/M was considered. But it may have been. As far as I can recall, the 6502 did not have a direct equivalent to CP/M back then. There was FLEX for the 6800, and then later on a version ...
To be fair, the 6809 came along a lot later, and because it was late to the party, and hence not established (so not as cheap) only made it into a small number of computer models.
This is probably more of a general Z80 question rather than applying to the Spectrum specifically, but do you think when Zilog designed and implemented the Z80's instructions and assigned them to either 1 or more byte opcodes that they always made the right choice? I'm not really talking about hypo...
Okay, best if we calm down. Right, so there are some points I want to comment on. First off, we now know far more about how high speed digital signals are affected on PCBs now, compared to the 1980s. And Sinclair did have problems. Yes, the ZX Spectrum was okay, but the QL board had to be redesigned...
I'm curious to know whether the Spectrum can make use of a 2nd joystick button (or Master System pad buttons for example)? As Andy says, it depends on the actual joystick interface. By this, I mean both the type and the actual revision/version. This is especially relevant for Kempston or Kempston c...