have an extra M105 + M7821 unibus card?

Tony Duell ard at p850ug1.demon.co.uk
Tue Jan 31 16:06:21 CST 2006

> Turns out the RX02 emulator needs an M105 and M7821 single height UNIBUS
> card to work.
> Anyone have an extra M105 and M7821?  
> I've never seen one of these, but that doesn't mean much.  Are they common?

They used to be very common. Original Unibus SPC cards were dual height 
and fitted into connectors C and D of the slot. You put an M105 address 
selector in connector E and an M782 (or M7820, M7821) interrupt logic 
board in connector F

The M105 is the address selctor. It decodes the address from the Unibus, 
generates SSYN as appropriate and supplies 4 decoded regsiter select 
lines and read/write lines to the peripjheral controller. The M7821 is 
the interrupt logic, it handles the bua master part of the interrupt 
sequence, supplies the vector, etc.

I haev no idea where you'd find one now. 'In DrARD's junk box' is not a 
useful answer, although true. I also have (I think)  some 3rd party dual 
height boards that fit into connectors E and F and perform both 

> Also, does any one have Schematics for the M105 and M7821?  I looked on
> bitsavers and did not find anything.

Try looking in the printsets for early SPC devices (KL11, PC11, DR11-A, 
etc). Some of those should include the M105 and M7821 schematics. 


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