HP2648A terminal

[Tony Duell]

> 
> First off, I meant to write DEC VT-11, not 1350.
> 
> As for digital versus analog vector generators, there is a vast difference.
> 
> And this is not like the difference between microprogrammed and random
> logic designs!
> 
> A digital vector generator uses counters that drive DAC's, each counter
> is clocked at a rate that controls the slope of the vector.  Most often
> binary rate multipliers are used to divide a fixed clock down to the rate
> needed to clock the counters up or down at the rate needed to draw
> at the desired angle.
> 
> An analog vector generator on the other hand will recharge a high
> quality capacitor (often compensated).  Once the X and Y axis DACS
> have charged these caps to the vector starting point voltages, the DAC's
> are updated with the vector end-point values an analog switching then
> causes the caps to charge or discharge to the new values.

Yes, thsoe are the definitions I assumed to.

The HP1350 is most certainly a digital vector generator by that 
definition. I've just looked at the official operating/service manual. 
The DACs are driven by counters, clocked by rate multipliers, etc. 


> Does the VT-11 have a keyboard port?

Not really. There's a keuboard connector at the back of the monitor used 
with the VT11, the signals from that (2 wires IIRC) just go down the 
cable to one of the VT11 boards and end up on backplane pins. In the VT11 
configuration (the 3 boards in a 4 slot backplane, to plug into the 
Unibus of a PDP11), these pins are not used. In the GT40 configuration 
(graphics terminal using these 3 boards, PDP11/05 processor boards, core 
memory, serial interdace in a 9 slot backplane, fitted into the 5.25" 
PDP11/05 cabinet, with a real frontpanel), the keboard uses the UART on 
the CPU board set, the appropriate pins are wired across the backplane.

-tony