Spectrum Computing

That may be what we'd all like to be true, but the reality is different. You caught me with my pants down, Mr. Feuerbach. Many of the decisions they made make it much harder for hackers, and edge connector hardware designers :) Doubtlessly. But were they "After careful consideration we'd rathe...

But it would have pushed up costs. Adding any extra hardware would have pushed up manufacturing costs. As would have better software. So, don't add it, just make the machine flexible enough to be able to add it later. Then sell it. Maybe you need a few lines more on the edge connector. And here's y...

I could never understand why in beginner's threads like this one people are suggesting advanced solutions which involve assembler etc. You don't help the poster this way, just make him confused. I think this is purely cultural. BASIC is a descendent of FORTRAN, a language aimed at mathematicians do...

Even a software solution costs in terms of programmer time and, potentially, ROM space. Of course. Same for the ULA modification. Even if there is space, you have to do the work, to fill it. Sinclair were so cheap and on such a tight schedule ... "Tight schedule" elsewhere known as "...

It was "can we do this cheaper? And what level of capability can we get away with?" which explains how the beeper came to be. "... what level of capability can we get away with?" is exactly what I'm talking about. You could have impressive sound for cheap. No external alteration...

1bvl109 wrote: ↑Tue Jul 16, 2019 5:39 pm I wondered, why, if the Z80 has to produce the sound anyway and execution of BASIC had to been stopped for that purpose, the didn't they use pwm.

Umm sorry. This should of course read ... why didn't they use pwm.

If audio quality had been seen as important, they would have stuck an actual sound chip in it. The simple ability to make some noise at low a cost as possible met their own low bar. But concerning pwm the investment would be only in software. What I'm saying is, they are not squeezing the max out o...

You’re forgetting that Sinclair wanted cheap and simple... Well I don't know, how much space the ULA actually offered, but some things seem to be caused more by rushed-to-the-market then by we-can-t'afford-the-hardware. Why provide extra hardware when the CPU can bit-bash a single bit (pin) control...

... the sound generation shares the same circuit as the tape output, and surmises it was done that way for efficiency (needing less logic gates in the ULA, which means more room to fit other functionality in). SOUNDS reasonable. But wouldn't it have been possible, to send, say 4 or 5 bits out throu...

80K of RAM would've been insanely expensive in 1982, certainly not something that would have been on the radar for a dirt cheap home computing device. I'm not so sure about this. Most of the ZX81 guys i knew bought 16K, the others bought 64K. For purpose of dirt cheap the Spectrum was at a factor o...

The ULA generates the control signals for the "lower" RAM accesses (/RAS, /CAS and the control for the address multiplexers) which in turn control the DRAM chips. So what happens if the CPU writes data just as the ULA sets up an address to read screen data? Will the write data go to an ad...

1024MAK wrote: ↑Mon Jul 15, 2019 6:29 pm BEEP uses the ULA / gate array and is available on all ZX Spectrum models.

I wondered, why, if the Z80 has to produce the sound anyway and execution of BASIC had to been stopped for that purpose, the didn't they use pwm. Maybe this would not have worked to well for higher frequencies, but still.

1024MAK wrote: ↑Wed Jul 03, 2019 7:45 am Yes, that is an error, R37 should have one end connected to 0V/GND.

Relates to the position of the component leads on the board, BK - back, FT - front, RT - right, LT - left...

Thank you captain. Heading for the alpha quadrant. Course set.

In this case, it wouldn't make much difference to run in "FAST mode". Well than. Thanks for the explanation. If you have an Assembly routine that needs to perform a CPU intensive task without updating the screen, all you need to do is compile this routine to an address above 32768 (i.e. t...

Even when there is contention (which by the way, only occurs between memory addresses 0x4000 and 0x7FFF plus any ULA I/O address) the delay to the Z80 CPU is not very significant compared to the loss of processing on a ZX81 I see. As all the BASIC system variables are fixed in the lower 16k, I thou...

Tis quite an interesting thought although I do not fully understand all the details but you're (I think?) saying no memory contention so it all runs 'same speed' wise yes ? :) Yes, exactly. While it was a quite noticeable difference on the ZX81, I wonder whether it would have been worth it on the S...

There is this thread about fixing the issue 3B to 4B schematics https://spectrumcomputing.co.uk/forums/viewtopic.php?f=22&t=1528&p=21755&hilit=Issue+2+schematics#p21755 However there also seems to be an error in the issue 2 schematics linked there http://www.retroisle.com/sinclair/zxspec...

If I remember correctly, Sinclair's position on a missing FAST mode in a computer which turned out to be renamed the "ZX Spectrum" was that it already is running in FAST mode all the time. If I understand correctly, it's true that in the ZX81 the Z80A had to serve as a counter for the SLC,...

Thanks to everyone, especially R-Tape who detected my fishing for consolation and delivered.
Seems I'll have to stray far of the usual MM/JW-Look or look again into conjuring up a NMI-driving-oscillater to slow things down. I see another question raising here, but it should be put somewhere else.

Ok, Here's my confession. I never got very far in this games.Yes, yes i know, these aren't even the hardest game this little machine had to offer, but anyway. Do the experts here have anything to recommand, preferably for the 48k? Also I never could make up my mind, if this is a game you should play...

Thanks.

As can be seen from https://skoolkit.ca/disassemblies/rom/asm/5615.html this simply performs a EXX RET in the original 48K-ROM and does all kinds of strange things. https://skoolkit.ca/disassemblies/rom/asm/13491.html warns "For a successful return to BASIC, HL' must on exit from the machine co...

Fortunately you don't need any fancy kind of randomness, only unforeseeability. This is a 8-bit version of arkanoyed's proposal http://www.z80.info/pseudo-random.txt and this is the theory with some code in Phyton and Pascal which should be transferable to BASIC. Besides 1) the frames counter and 2)...