CDC 6600 display character generation

[Paul Koning]

> On Jun 6, 2018, at 12:31 PM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
> 
>> From: Toby Thain
> 
>> It's suggested there (without any proof though) that the CDC used a
>> Fourier process
>> ...
>> I'd be very interested to know what you find out about the circuitry.
> 
> Someone very kindly pointed me at:
> 
>  http://www.bitsavers.org/pdf/cdc/cyber/cyber_70/fieldEngr/60125000C_6602_6603_6622_6681_6682_Data_Channel_Diagrams_Dec65.pdf
> 
> (although why it's in the Cyber70 folder, I'm not quite sure :-). I don't
> completely understand it (it's only drawings, no text, and the notation is
> unfamiliar), but I think I get the general drift - and it's pretty baroque!

The notation is explained at the start of http://www.bitsavers.org/pdf/cdc/cyber/cyber_70/fieldEngr/60119300BT_6600_Diagrams_and_Circuit_Description_Vol1_Jan68.pdf

It's pretty straightforward: circles for AND, squares for OR.  Arrowhead means inversion.  They call the basic logic element "NAND" but it is NOR in the usual terminology (it's "invert then AND" while "NAND" as normally used means "AND then invert").  The logic diagrams show both AND and OR boxes because they are drawn to show the logic operations via De Morgan's law, not the actual circuits.

The logic modules are drawn as larger rectangles with the circuit elements in them.  A circle at the module outline is a twisted pair input or output (connection within the chassis).  A double circle (figure 8 lying on its side) is a coax input or output, for between-chassis or external connections.

Finally, circuit boxes with an X or dot in them are "special circuits", i.e., not plain logic.  The AF module, which is the D/A converter for the display controller, has these, as do the core memory sense amplifier modules.

	paul