STE video chip

[Badwolf]

(EDIT : yes, shameless self quoting of my work :D )

No, thank you for doing that, as I had completely forgotten I had a copy of your repo here! :-)

BW

[Steve]

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?

PXL_20220111_105516032.jpg

PXL_20220111_110024530.jpg

PXL_20220111_112742693.MP.jpg

PXL_20220111_112137236.jpg

[exxos]

Are you using x10 probe ?

EDIT:

Eitherway it looks out of sync with the C301712, which is what I documented. So you need the other chip most likely.

[Steve]

Yes,

Here is one in 1X:

PXL_20220111_113526809.MP.jpg

[Steve]

@exxos The SN74F257 only outputs 2.5v clock, is that correct? Would it be better if it outputted 5v?

[exxos]

Use the cartridge port metalwork for the ground and see if that helps, that is what I used.

[exxos]

@exxos The SN74F257 only outputs 2.5v clock, is that correct? Would it be better if it outputted 5v?

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.

[sporniket]

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?

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 ?

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 )

[exxos]

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 ?

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.

Steve has the "buggy" shifter which causes problems on my machine. So there is nothing else to investigate other than swapping it.

[sporniket]

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 ?

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.

Steve has the "buggy" shifter which causes problems on my machine. So there is nothing else to investigate other than swapping it.

Thanks for the answers