>>>>> "Tony" == Tony Duell <ard_at_p850ug1.demon.co.uk> writes:
>> I assume Sellam means a device which will present the time and
>> possible date maintained independently of the CPU. There I would
>> agree I we are into the mini era if not the micro.... There was an
>> add on RTC clock card for the PDP-11 (but Sellam specified
>> "built-in" ;-) If it does not
Tony> I don't rememebr a clock card for the '11 -- there were
Tony> line-time and programmable interrupt cards that gave a periodic
Tony> 'heatbeat', and that's what DEC normally regarded as a real
Tony> time clock...
The standard "clock" was the KW11-L -- just an interrupt tied to the
mains frequency. That was a very common option in early machines and
became a builtin feature of the CPU assembly in later ones.
Some systems, for example those used in real time control, might have
a KW11-P -- which lets you program the interrupt rate from a choice of
three input oscillators (100 kHz, 10 kHz, and mains, if I remember
right) along with a programmable divider. The 11/20 on which I
learned in the college physics department had such a beast, and I
added support for it into RT11 BASIC.
There's the KW11-W, which turns out not to be the TOY clock I thought
it was -- it's a watchdog. RSX systems sometimes used that.
Finally, there's the KW11-C which is what I was trying to remember.
That is a TOY clock. See
http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/decus/110721.html
for example. I suspect it may have been a CSS ("Computer Special
Systems" -- the custom and low volume department of DEC) creation,
which would be a reason for it not being well known.
paul
Received on Fri Jul 30 2004 - 08:24:22 BST