zuiko21
Well-known member
I've been thinking about this for a long time... my idea is to keep the SE/30 (or any other Mac without soft-power) permanently switched on, but plugged into an external switching box, which would be little more than a relay, a flip-flop and a tiny PSU for them.
This box needs two control lines from the Mac: the turn-on signal comes from the ADB keyboard, of course. Since the SE/30 has two ADB connectors, and only one (keyboard & mouse in series) is normally used, this is quite easy to get -- provided the PSW lines on both ports are tied together, which they aren't... but that's easily solved by a jumper wire. Other Macs with a single ADB port may use a small extension in order to derive this signal -- again an easy task, because ADB uses the same 4-pin Mini-DIN connector as S-Video (S-VHS)
Then we need the turn-off signal... Mac II series computers' PSUs use a /PFW line from the start-up circuit, which in turn is derived from VIA2's PB2 line. Upon issuing the Shutdown command, once the Mac is ready to be turned off, this line goes from +5 V down to 0, signalling the PSU to turn off. Then, the Mac will show the It's safe to switch off your Macintosh message, but if the PSU/start-up circuit works as intended, it won't go that far I tried this on a IIx (which in a way has similar hardware as the SE/30, plus the very same ROM) with a hacked PSU in order to stay on regardless of the /PFW line status, and PB2 went to zero as soon as the aforementioned message appeared -- as expected.
Back to the SE/30, theoretically this line should be present at pin 81 (C1) of the PDS slot, but actually won't reach there -- quite understandable since the SE/30 has no use for it. Then I searched for a point in the mobo directly connected to VIA2's PB2, and I found it. The only remaining thing would be taking it outside -- pin 5 of the external floppy connector is unused and not connected, so it seems quite suitable for the task.
I have marked my SE/30 board with the location of the required jumpers: there should be one wire from P to 5, and another one joining both K points.
For obvious reasons, I have designed the external box to stay on whenever the control link is lost. One of the ground pins on the FDD connector is used as a presence detect line.
But then I repeated the IIx test on the SE/30 and... that damned PB2 line stays on forever, even with the It's safe to switch off... on display! 8-o
Not sure if I'm missing anything... I am aware that, despite sharing the same ROM code, the SE/30, IIx and IIcx give different Gestalt codes -- it's computed from a couple of hardwired VIA ports. Maybe the programmed PB2 value on shutdown is taken from those bits? Or is it simply disabled upon detecting unsupported (soft-power wise) hardware? I was using a custom, ahem, IIci ROM anyway If the reason behind is the latter, it shouldn't be too difficult to write a small system extension in order to enable this soft-power feature, but I have zero experience writing Mac-specific software at all
Any ideas?
This box needs two control lines from the Mac: the turn-on signal comes from the ADB keyboard, of course. Since the SE/30 has two ADB connectors, and only one (keyboard & mouse in series) is normally used, this is quite easy to get -- provided the PSW lines on both ports are tied together, which they aren't... but that's easily solved by a jumper wire. Other Macs with a single ADB port may use a small extension in order to derive this signal -- again an easy task, because ADB uses the same 4-pin Mini-DIN connector as S-Video (S-VHS)
Then we need the turn-off signal... Mac II series computers' PSUs use a /PFW line from the start-up circuit, which in turn is derived from VIA2's PB2 line. Upon issuing the Shutdown command, once the Mac is ready to be turned off, this line goes from +5 V down to 0, signalling the PSU to turn off. Then, the Mac will show the It's safe to switch off your Macintosh message, but if the PSU/start-up circuit works as intended, it won't go that far I tried this on a IIx (which in a way has similar hardware as the SE/30, plus the very same ROM) with a hacked PSU in order to stay on regardless of the /PFW line status, and PB2 went to zero as soon as the aforementioned message appeared -- as expected.
Back to the SE/30, theoretically this line should be present at pin 81 (C1) of the PDS slot, but actually won't reach there -- quite understandable since the SE/30 has no use for it. Then I searched for a point in the mobo directly connected to VIA2's PB2, and I found it. The only remaining thing would be taking it outside -- pin 5 of the external floppy connector is unused and not connected, so it seems quite suitable for the task.
I have marked my SE/30 board with the location of the required jumpers: there should be one wire from P to 5, and another one joining both K points.
For obvious reasons, I have designed the external box to stay on whenever the control link is lost. One of the ground pins on the FDD connector is used as a presence detect line.
But then I repeated the IIx test on the SE/30 and... that damned PB2 line stays on forever, even with the It's safe to switch off... on display! 8-o
Not sure if I'm missing anything... I am aware that, despite sharing the same ROM code, the SE/30, IIx and IIcx give different Gestalt codes -- it's computed from a couple of hardwired VIA ports. Maybe the programmed PB2 value on shutdown is taken from those bits? Or is it simply disabled upon detecting unsupported (soft-power wise) hardware? I was using a custom, ahem, IIci ROM anyway If the reason behind is the latter, it shouldn't be too difficult to write a small system extension in order to enable this soft-power feature, but I have zero experience writing Mac-specific software at all
Any ideas?