I read that bus line #24 is conventionally allocated to -9v. Which boards require that?
AFAICS there is no standard allocation to line #23, yet Glitch's restoration PCB has a heavy trace there all of the way across to the extension connector.
I have a 574 Analog I/O board and there it appears that line #24 is expected to be allocated to -12v, and line #23 to +12v. The allocation of line #23 to +12v seems consistent with the heavy trace on Glitch's restoration board. But I haven't come across any documentation justifying either that use of bus line #23 or the heavy trace on the PCB.
Question #1: Is bus line #24 usage then inconsistent depending on the boards in a system, or is it always -9v (or unconnected) and the 574 is wrong to expect -12v there?
Question #2: Is bus line #23 usage for +12v documented anywhere? Is it known not to conflict with other use by other boards of that line?
It's a great backplane restoration. I want to make sure that I understand its nuances before proceeding :->!
Thank you.
paul
OSI 480 Backplane Power Lines
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pbirkel
- Posts: 34
- Joined: Mon Feb 27, 2017 8:06 am
Re: OSI 480 Backplane Power Lines
I've studied more schematics. At least the ones that I've looked at agree that +12v / -9v on lines #23 / #24 are the standard expectations, although I still can't find any documents declaring this to be so.
It appears that on the boards supporting RS-232 it was standard practice to use an asymmetric supply, which does meet the MC1488 specs (nominal -9v; max -15v).
The 574 is willing to let you jumper the -9v to the internal "-12v" distribution. Not using symmetric rails is "not nice" for either the ADC or DACs on that board; I don't see any reasonable board parts-configuration where that would be reasonable. However, OSI made it possible.
In my case the 6-pin Molex on the 574 that is used in a stand-alone configuration must have been the intended source of supply. I could do the same ... but it would be nice to keep power distribution on the backplane. Are there any particular rules to employing the uncommitted lines, e.g. line #22, for this purpose. Aside from Be Careful To Check All Of Your Boards, of course :->!
It appears that on the boards supporting RS-232 it was standard practice to use an asymmetric supply, which does meet the MC1488 specs (nominal -9v; max -15v).
The 574 is willing to let you jumper the -9v to the internal "-12v" distribution. Not using symmetric rails is "not nice" for either the ADC or DACs on that board; I don't see any reasonable board parts-configuration where that would be reasonable. However, OSI made it possible.
In my case the 6-pin Molex on the 574 that is used in a stand-alone configuration must have been the intended source of supply. I could do the same ... but it would be nice to keep power distribution on the backplane. Are there any particular rules to employing the uncommitted lines, e.g. line #22, for this purpose. Aside from Be Careful To Check All Of Your Boards, of course :->!