Subject: Re: Front Panel Variations on PDP8's

From: [email-masked] (Charles Lasner)
Date: 17 Feb 1994 02:01:16 GMT

In article <[email-masked]>,
Stephen Quigg <[email-masked]> wrote:
>
>  I'd like to start another thread, FRONT PANEL VARIATIONS ON PDP8's. For 
>instance, the 8e has at least 2 (not counting the MARS panel), depending
>on whether it has an 11 or 12 position switch. I never even noticed this until
>I tried swapping escutcheons and found that the switch didn't match the 
>markings on the panel. I prefer the 11 position panel (I think it's the older
>of the two) because it has vertical lines grouping the lamps into groups of
>3 to make life easier. 

Not to complicate things, let's right now stick to consoles of the 
Omnibus machines, as opposed to other -8's and -12's, and also colors of 
switches and silkscreens!

The standard 8/e panel comes in two variations.  The original indeed 
detents at nice intervals so that STATE and BUS are 180 degrees apart.  
The switch is actually a multiple magnetic reed assembly and the knob 
turns a small magnet on a plastic shaft.  The shaft is easily broken!  
Also, it can be turned indefinitely without stops.  Sometimes it's useful 
to set it to a non-position which is easily done.

Newer panels, or panels forced to be upgraded after the switch broke have 
a chincier rotary switch of conventional design with stops at the ends.  
The silk-screen lines have to be redrawn because the detents are a 
different number of degrees.

Early variant 8/f-m panels exist that were ECO'd from 8/e panels.  Some 
may even have the reed switch.  Most have the wafer rotary switch.  
Production panels all have the wafer.  The LED panel can be used in the 
8/e; there's even a lug to hang the unused 8V supply lead to!  The 8/e 
panel cannot be used in the 8/f-m because the switching power supply 
doesn't have that voltage tap available.

If you remove the 330 ohm pre-heat resistors, you can use LED's on the 
8/e panel.  Data Display Products makes an excellent replacement similar 
to the LED replacement DEC used in late-production RK05 drives.  The lamp 
has a built-in limiting resistor and uses the slide-in package.  (The 
pre-heat resistor must be removed else the brightness for 1 vs. 0 is 
indistinguishable.) If you are fortunate to have one of the TC08 status 
panels with sockets, the DDP LED is a direct replacement.  Color and 
intensity coming through the silkscreen dot are remarkably close to an 
incandescent bulb!

There is a double-height card for the Omnibus that functions as an SW 
switch for limited configurations, similar to that for the 8/m or an 8/a 
sans the octal readout panel ("linited function panel").  I've seen the 
card, but there's supposed to be a little panelette for it to be mounted 
near a power switch on a desk, etc.

Years ago, some company made a hand-held calculator-type front panel for 
the Omnibus.  A short-lived company designed a front panel that was meant 
to be between the console teletype and the Omnibus.  The card doubled as 
device 03/04 until the break key was hit.  At that point further 
keystrokes were directed at the front panel, not the -8.  Single-letter 
commands can access all registers and restart the -8, etc.  CESI got the 
rights to this card and expanded on it to produce the AFP8 or "ASCII 
Front Panel 8".  This card does the same as the earlier prototype, but 
also includes a real-time clock that is quite incompatible with all 
others but also does a lot more.  It includes a battery-driven 
clock/calendar chip to keep track of date/time as well as a tick 
interrupt, etc.  Also, the front panel function can address the extended 
memory functionality of the KT8A and the MEC8 (128K or 512K).

DEC produced low-volume ("Computer Special Systems") products that were a 
hardware breakpoint box (fetch/exec stop) and the "MARS" panel.  I have 
both panels, but alas, neither module to run them :-(.  The breakpoint 
module can stop the machine on any combination of FETCH to a 15-bit 
address or EXEC to a 15-bit address.  DECUS once published the prints of 
a dual-device of this type; that way you could have both types of trap 
simultaneously, etc.

There was a third-party company that produced a successful module called 
Computer Interface Systems, Inc.  It can trap on one match only similar 
to the DEC version.  The address is dialed up with 5 digit wheels.  The 
controls are available in a hand-held or panel-mounted variation that 
plugs into the breakpoint module itself.

If more than one panel (8/e and 8/a for instance, as on my own machine!) 
is present, be wary of the OR-ing of the switch register, and also of the 
indicators bits on the Omnibus.  Four of the available displays can only 
be generated by a unique combination of these bits, thus an incompatible 
display setting makes (at least one!) of the displays read the wrong 
register.

>I notice on the cover of one of the pdp8a small 
>computer handbooks (1975?) a picture of an 8a programmers console. This is
>the only picture I've seen where the keypad has round buttons (instead of 
>oval); also the layout of the lamps is a little different. Has anyone seen 
>this panel?
>
Any of these variations apply to the 11/34 family?

cjl