tech58761
Experienced Member
After getting my hands on those Universal Instruments boards (and having moved most along to new homes by now) I got to thinking about two in particular.
I've decided to see about laying out replacement boards and sharing the Gerbers for those who may want to build one for their PDP system.
Looking at the schematics, I see three ICs were used for interfacing the board to the backplane.
Input-only lines are fed through a National DS8837 IC with its control lines wired 'always on'.
Bidirectional lines (the system address / data bus) are fed through a quartet of National DS8838 ICs.
Output-only lines are fed through a 7438 (which is surprisingly still available from TI - is that the last straight TTL part still in regular production??)
First question - are there modern equivalents of the DS8837 / DS8838? I tried looking at the publicly available docs for the UniBone / QBone, but the copies I found seemed to be partial schematics, so am not clear.
Now, one of the two boards I was interested in laying out a replacement is the bootstrap board (A/N 27514) - I could see this being handy to save the time and effort in keying in the bootloader / minimizing wear and tear on punched tape readers.
As is, the board uses a pair of TMS2516 (2716), and it seems that the 2764 / 2864 would be more available these days (in fact, I may even have a tube of unused / lightly used 2764s kicking around).
The design currently uses address lines A0-A9 (A10 tied to ground), and stepping up to the 2764 or 2864 would add lines A11 and A12.
Second question - it would be just a matter of adding a 3-position DIP switch and pull-up resistors to provide for up to 8 sets of bootstrap images, correct? The system looks at only A0-A9, so it shouldn't matter address-wise, right?
The other board I was looking at is the power sequencer board (A/N 4127304), which has been pointed out would allow the use of standard Meanwell supplies instead of the DEC power supply (like the H786 in the 11/03 chassis).
The changes I was looking at included adding the grant continuity traces and relocating the AC power (25VAC center-tap) to a Phoenix connector on the front edge of the board.
The only issue I see is the filter caps for the on-board 7912 and 7805 regulators.
Third question - can someone direct me to the relevant spec for height limits on the Qbus boards? I obviously would need to select appropriately sized electrolytic caps if possible.
Lastly, I was looking at the machine interface board (A/N 18013), I see something that is a little confusing - this is not a board I'd be looking to reproduce, rather, what degree of caution is necessary in using this board.
The issue I see is that one ground trace is run to pad BS1 instead of BT1 as would be expected.
Any thoughts appreciated.
I've decided to see about laying out replacement boards and sharing the Gerbers for those who may want to build one for their PDP system.
Looking at the schematics, I see three ICs were used for interfacing the board to the backplane.
Input-only lines are fed through a National DS8837 IC with its control lines wired 'always on'.
Bidirectional lines (the system address / data bus) are fed through a quartet of National DS8838 ICs.
Output-only lines are fed through a 7438 (which is surprisingly still available from TI - is that the last straight TTL part still in regular production??)
First question - are there modern equivalents of the DS8837 / DS8838? I tried looking at the publicly available docs for the UniBone / QBone, but the copies I found seemed to be partial schematics, so am not clear.
Now, one of the two boards I was interested in laying out a replacement is the bootstrap board (A/N 27514) - I could see this being handy to save the time and effort in keying in the bootloader / minimizing wear and tear on punched tape readers.
As is, the board uses a pair of TMS2516 (2716), and it seems that the 2764 / 2864 would be more available these days (in fact, I may even have a tube of unused / lightly used 2764s kicking around).
The design currently uses address lines A0-A9 (A10 tied to ground), and stepping up to the 2764 or 2864 would add lines A11 and A12.
Second question - it would be just a matter of adding a 3-position DIP switch and pull-up resistors to provide for up to 8 sets of bootstrap images, correct? The system looks at only A0-A9, so it shouldn't matter address-wise, right?
The other board I was looking at is the power sequencer board (A/N 4127304), which has been pointed out would allow the use of standard Meanwell supplies instead of the DEC power supply (like the H786 in the 11/03 chassis).
The changes I was looking at included adding the grant continuity traces and relocating the AC power (25VAC center-tap) to a Phoenix connector on the front edge of the board.
The only issue I see is the filter caps for the on-board 7912 and 7805 regulators.
Third question - can someone direct me to the relevant spec for height limits on the Qbus boards? I obviously would need to select appropriately sized electrolytic caps if possible.
Lastly, I was looking at the machine interface board (A/N 18013), I see something that is a little confusing - this is not a board I'd be looking to reproduce, rather, what degree of caution is necessary in using this board.
The issue I see is that one ground trace is run to pad BS1 instead of BT1 as would be expected.
Any thoughts appreciated.
