exxos's Atari, Amiga & retro forum

I think the only thing which uses 12V is on the monitor port now.. Of course no need for 12V for floppy drive anymore..

So really just thinking ahead that a 5V only PSU could probably be used ultimately.. ?

Does anything actually use the -12V in the ST ?

I searched for a 12V point in my ST for a while, and the only one i found was on the monitor port,
i connected a cooling fan to it.

SolderGirl wrote: ↑Fri Aug 10, 2018 6:18 pm Does anything actually use the -12V in the ST ?

I searched for a 12V point in my ST for a while, and the only one i found was on the monitor port,
i connected a cooling fan to it.

Serial port, right?

troed wrote: ↑Fri Aug 10, 2018 6:29 pm

SolderGirl wrote: ↑Fri Aug 10, 2018 6:18 pm Does anything actually use the -12V in the ST ?

I searched for a 12V point in my ST for a while, and the only one i found was on the monitor port,
i connected a cooling fan to it.

Serial port, right?

Yes and no..

https://www.exxosforum.co.uk/forum/viewt ... ?f=19&t=15

RS232 would normally need -12 (generated on the motherboard) and 12V from the PSU...

RS232 circuit was re-designed and only needs a single 5V supply now... It saved a huge lot of parts on the board in doing that...

EDIT: Quick look at the old -12V gen also seems to generate the +12 as well...

Ehum. Ubeswitch uses 12V. But one kan feed the switch using the isp header as well. 5V will do there. Otherwise one could remove the regulator and add a view between two pads.

There is a chance that UBEswitch will be fine with 5V on 12V rail... As for floppies - even the Sony FDD used on latter STes didn't use 12V.

The +/-12V has been used for RS232 only on early STs with external power adapter.

Negative rails on the STF were generated with a switchmode inverter on the MB . However they are not needed with the new STF as the RS232 chip generates negative voltages internally. This saved a lot of parts on the STF MB..

12V As I think Icky mentioned somewhere a few days ago, that scart uses 5V,12V for switching aspect ratios.

So while we could just output 5V on the pin directly to power the UBE for example, there is still the issue of scart switching to wrong aspect ratio use if the voltage is only outputting 5V.. Is actually pretty annoying as it basically means we need a 12V rail for pretty much no reason.

It's possible there may be a small integrated inverter which we could use to generate 12V. Then it would allow smaller power supply to be used would be 5V only.

As another thought, is the GPIO pin actually used for anything ? Could just swap that for 5V output to power UBE and external stuff instead.