22 Nov
2006
22 Nov
'06
11:51 a.m.
Ethan Dicks wrote:
Yes, though it can use an 8MHz input via the on-board prescaler on one
channel.
On 11/23/06, Gordon JC Pearce <gordon at
gjcp.net> wrote:
No, it *is* 2MHz. The confusion is because if you use the on-chip
oscillator, you use a crystal that's 4x the E clock frequency, so an
8MHz crystal for a 2MHz clock.
J Blaser wrote:
Hmm... I would have thought that it was a 2MHz part, but some googling
does show the B variant clocked at 8MHz. If that's the case, I wonder
if it's possible to overclock Henk's "Real Console". I've collected a number of Q-bus boards for
PDP-11s and/or VAXen...
Well, on the CompuServe board, there is a 68B09 which is (I believe) an
8MHz version of the 6809. There's a
68B40 which I think is a CTC (counter/timer)...
That it is. It's also known as a "PTM" - Programmable Timer Module.
Some light digging around seems to show that it's a 2MHz part. I don't think CompuServe made 6809-based Qbus
CPUs, so I'd think this
is some sort of peripheral, but it's functionality is not obvious to
me. So far, we know what CPU it has, it's local SRAM space (16K), and
that it has a timer. It must be getting its code from the host since
I can't spot any ROMs, but once that load happens, _then_ what does it
do?
No guesses from me either, but there's what appears to be a small
ceramic TTL PROM near the middle of the board (middle row, 7th from the
right).
--
Pete Peter Turnbull
Network Manager
University of York