PDP-8 question...

16 Oct 2000

...

 Well, mine is set for fields 4-7, but I dont have
any docs. And since
its working i'm hesitant to tear it apart.  
 Tear it apart?  This one is only two boards at the top one is the only 
 one with significant logic and drivers.  the other is the diode matrix 
 and core mat.  There is a DIP socket in the middle (mine has 
 nothing in it) and a set of three posts one dip above it.  If you 
 could tell me what you have there it would help. 

The 16 pin DIP socket has a "black box" plugged into it. Hmm, popping
that box open reveals the expected jumpers.

Looking down at the jumpers, the upper left corner is pin 1, upper right
is pin 16, I have 4 wires installed:

 pin 5 - pin 14
 pin 6 - pin 13
 pin 7 - pin 12
 pin 8 - pin 11

My board is set to cover fields 4 - 7. 

My guess would be that the 3 EMA bits are decoded into 8 lines, and are
present on pins 1 - 8, corresponding to DEC field terminology 0 - 7, 
which makes obvious sense since pins 1 - 8 are on one side of the 
DIP jumper, and that pins 11 - 14 are the individual 4Kx12 field
select jumpers. 

-Lawrence LeMay

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PDP-8 question...