[time-nuts] 60Hz mains clocking in computers

[David I. Emery]

On Sat, Dec 12, 2009 at 11:29:31PM -0800, J. Forster wrote:
> I'm not so sure about the Nova 1200. I think all the Novas had the RTC was
> on a standard I/O board, along with the serial interface, PTR, PTP. I
> remember two crystals, one 16.000 KHz for the clock. The other was for the
> Baud Rate generator, somewhere about 1 MHz. A minimal system had 3 cards
> (CPU, Memory, and I/O)

	No 50/60 Hz interrupt was standard on any DG machine that I
remember. I do remember some on early DEC equipment.  And yes they had a
Xtal RTC.

	I do remember the early DG basic IO boards had a big LF crystal
for the baud rate generation, but I think a later version of the design
used a baud rate generator IC and a much smaller (and cheaper) crystal
or canned crystal oscillator along with a real UART.

	OS timing was based on classic real time xtal based interrupts,
not the power line.

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."