Re: STE video chip
Posted: 11 Jan 2022 11:13
No, thank you for doing that, as I had completely forgotten I had a copy of your repo here! :-)
BW
BW
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No, thank you for doing that, as I had completely forgotten I had a copy of your repo here! :-)
Yes, but in the MHz range the voltage drops anyway. The buffered clock on the CPU goes from like 1-2V, its a wonder it even works at that. But the loading of the probes taints results because of all the loading. It could be the probes you are using causing the issue. It is a bit of a minefield unfortunately.Steve wrote: 11 Jan 2022 13:13 @exxos The SN74F257 only outputs 2.5v clock, is that correct? Would it be better if it outputted 5v?
The SN74F257 select the clock source (for the genlock), your motherboard seems to be a PAL system as I don't see U402. So for a starter the 32Mhz clock is not a signal straight from an oscillator, which may not help for a booster ?Steve wrote: 11 Jan 2022 12:47 Just testing an STe with the C301712-001 shifter and has a SN74F257 for 32mhz. This Machine was too unstable to run the 32mhz exxos booster. HC CPU installed.
Ch1 is on 32Mhz Ch2 was on 8Mhz CPU clock. Photos of how I wired it up too.
The 32mhz looks terrible doesn't it?
sporniket wrote: 11 Jan 2022 10:07 The "MC" is proxyed by the selector U405(p 21 of my schematics), that select between a "32MHz" clock, either by a simple 32MHz oscillator on non-PAL systems (the exact frequency depends whether the it is for NTSC or not), or a 32 MHz oscillateur modulated by a line phase generated by a sub-carrier clock for PAL systems (see p.8), either by external clock (genlock) from the video port (see p. 21)
(EDIT : yes, shameless self quoting of my work :D )
The 32Mhz clock is buffered via the F257 which is what the booster has always used. Using direct from the osc probably won't work.sporniket wrote: 11 Jan 2022 13:20 The SN74F257 select the clock source (for the genlock), your motherboard seems to be a PAL system as I don't see U402. So for a starter the 32Mhz clock is not a signal straight from an oscillator, which may not help for a booster ?
Thanks for the answersexxos wrote: 11 Jan 2022 13:28The 32Mhz clock is buffered via the F257 which is what the booster has always used. Using direct from the osc probably won't work.sporniket wrote: 11 Jan 2022 13:20 The SN74F257 select the clock source (for the genlock), your motherboard seems to be a PAL system as I don't see U402. So for a starter the 32Mhz clock is not a signal straight from an oscillator, which may not help for a booster ?
Steve has the "buggy" shifter which causes problems on my machine. So there is nothing else to investigate other than swapping it.