28 Dec
2005
28 Dec
'05
7:23 p.m.
After pulling out my hair for a while trying to get my PDP-11 to
talk to me, I finally discovered that the master clock (26.667 MHz
crystal oscillator) is dead. (KDF-11BA CPU board).
Those metal-package oscillators are very common and inexpensive
(around $2), but I can't find one in that exact frequency. 25,
25.175 and 27 MHz units are available. Semi-custom ones aren't
terribly much more expensive (~ $15) but have longer lead times.
Is there anything in the circuitry that can't be run a little
slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
every last MIPS out of it.
thanks
Charles
28 Dec
28 Dec
7:35 p.m.
You can order oscillators programmed with custom frequencies from
DigiKey, assuming you're speaking of oscillators and not a crystal (I
have someone at work who routinely interchanges the terms, and it drives
me up the wall). They may not be in metal cans, but they are available
in the same foot print. DigiKey can have them to you as fast as you
want to pay for shipping.
--jc
Charles wrote:
After pulling out my hair for a while trying to get my
PDP-11 to
talk to me, I finally discovered that the master clock (26.667 MHz
crystal oscillator) is dead. (KDF-11BA CPU board).
Those metal-package oscillators are very common and inexpensive
(around $2), but I can't find one in that exact frequency. 25,
25.175 and 27 MHz units are available. Semi-custom ones aren't
terribly much more expensive (~ $15) but have longer lead times.
Is there anything in the circuitry that can't be run a little
slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
every last MIPS out of it.
thanks
Charles
8:38 p.m.
I've used the Digiikey service to get a custom frequency (20.2752MHz,
4x the 5.0688MHz clock frequency of a DL11-W). A little pricey (~$8
each), but worked just as expected.
For your application though anything in the 25-27MHz should work just
fine. If you are really adventurous put in a socket and get a few
frequencies up to 33MHz or so and see how fast you can really go.
Clock chipping an oscillator based PDP-11 is a lot more
straightforward than an older tapped delay line design like a 34, 44,
etc.
On Dec 28, 2005, at 4:35 PM, J.C. Wren wrote:
You can order oscillators programmed with custom
frequencies
from DigiKey, assuming you're speaking of oscillators and not a
crystal (I have someone at work who routinely interchanges the
terms, and it drives me up the wall). They may not be in metal
cans, but they are available in the same foot print. DigiKey can
have them to you as fast as you want to pay for shipping.
--jc
Charles wrote:
> After pulling out my hair for a while trying to get my PDP-11 to
> talk to me, I finally discovered that the master clock (26.667 MHz
> crystal oscillator) is dead. (KDF-11BA CPU board).
>
> Those metal-package oscillators are very common and inexpensive
> (around $2), but I can't find one in that exact frequency. 25,
> 25.175 and 27 MHz units are available. Semi-custom ones aren't
> terribly much more expensive (~ $15) but have longer lead times.
>
> Is there anything in the circuitry that can't be run a little
> slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
> every last MIPS out of it.
>
> thanks
> Charles
>
>
29 Dec
29 Dec
7:17 a.m.
After pulling out my hair for a while trying to get my PDP-11 to
talk to me, I finally discovered that the master clock (26.667 MHz
crystal oscillator) is dead. (KDF-11BA CPU board).
Those metal-package oscillators are very common and inexpensive
(around $2), but I can't find one in that exact frequency. 25,
25.175 and 27 MHz units are available. Semi-custom ones aren't
terribly much more expensive (~ $15) but have longer lead times.
Is there anything in the circuitry that can't be run a little
slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
every last MIPS out of it.
I've not actually worked on this machine, but I know that the old Unibus
11's have nothing that depends on the exact freqeucny of the Xtal. I
would be suprised if any of the ones you mentioned wouldn't work fine.
-tony
9:37 a.m.
Charles wrote:
Is there anything in the circuitry that can't be
run a little
slower (or 1.2% faster, 27 MHz)? I'm not worried about squeezing
every last MIPS out of it.
27MHz will be close enough. I don't think anything will be too upset at
slightly altered timings. If you notice any weirdness, go down the
route of getting a custom crystal cut if you're *sure* it's because the
clock is a tiny bit faster.
Gordon.
1:15 p.m.
Rumor has it that Charles may have mentioned these words:
After pulling out my hair for a while trying to get my
PDP-11 to
talk to me, I finally discovered that the master clock (26.667 MHz
crystal oscillator) is dead. (KDF-11BA CPU board).
Those metal-package oscillators are very common and inexpensive
(around $2), but I can't find one in that exact frequency. 25,
25.175 and 27 MHz units are available.
I are a dumby when it comes to PDPs, but if you're worried about
overclocking, Mouser has 26Mhz oscillators on the shelf - it's closer than
25.x Mhz.
Page 665 in the catalog, IIRC. Their search utility is somewhat OK, too, at
least to narrow down a page or two of the catalog, then you can view each
page as a PDF. Not a bad system, really.
[[ A page or two before that, they have Fox custom oscillators as well - I
don't know if they're a better price than Digikey or not... ]]
As always, just a satisfied customer; no other affiliations. ;-)
HTH,
Roger "Merch" Merchberger
--
Roger "Merch" Merchberger -- SysAdmin, Iceberg Computers
zmerch at 30below.com
Hi! I am a .signature virus. Copy me into your .signature to join in!
1:32 p.m.
----- Original Message -----
From: "Roger Merchberger" <zmerch at 30below.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Thursday, December 29, 2005 7:15 PM
Subject: Re: Changing the clock frequency slightly (PDP-11)?
Rumor has it that Charles may have mentioned these
words:
The 27 MHZ unit is only 333 Hz off,
which is 0.00125%, if I have my decimal
point correct.
A common trick to change the frequence of a crystal, is to put a capacitor
in parallel with it.
Nico
After pulling out my hair for a while trying to
get my PDP-11 to
talk to me, I finally discovered that the master clock (26.667 MHz
crystal oscillator) is dead. (KDF-11BA CPU board).
Those metal-package oscillators are very common and inexpensive
(around $2), but I can't find one in that exact frequency. 25,
25.175 and 27 MHz units are available.
1:32 p.m.
> (26.667
MHz crystal oscillator)
> 25, 25.175 and 27 MHz units are available.
The 27 MHZ unit is only 333 Hz off,
which is 0.00125%, if I have my decimal point correct.
1.25% (well, 1.248734+%) - 333Hz would be (approximately) 0.00125%, but
333KHz is 1000 times that.
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