Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!rpi!jtwarden
From: jtwarden@pawl.rpi.edu (Joseph T. Warden)
Newsgroups: comp.sys.mac
Subject: Re: PMMU Speeds
Message-ID: <1989Oct6.004657.20614@rpi.edu>
Date: 6 Oct 89 00:46:57 GMT
References: <15944@dartvax.Dartmouth.EDU>
Organization: Rensselaer Polytechnic Institute, Troy NY
Lines: 35
Distribution:usa
Summary:The speed is designated on the chip

In <15944@dartvax.Dartmouth.EDU> thomas@eleazar.dartmouth.edu (Thomas Summerall) writes:
>
>Hi Folks!  It looks our deparment's Mac II is about to be released from memory
>bondage!  I have in front of me a 68851 PMMU sent to us by Motorola.  Here's the
>problem:  I don't know if it is the right speed.
>
>Do PMMU's come in different speeds?  If so, how do I know what speed this one
>is?  I didn't specify 16Mhz in the request letter, so I'm not sure, and I don't
>want to fry my Mac in the process of installation...
>
>
>Thanks...
>Thomas Summerall
>thomas@eleazar.dartmouth.edu

The designation for the speed is part of the part number for the chip
as is stenciled on the top. You should see a list of numbers including 
(my memory fails me here) 16RC (or something like that). I also
received a part from Motorola (Thanks so much Chet and crew) and it
was a 16 MHz part. MacEnvy recognized its presence so I am assuming
all is well.

Caution - when installing (1) ground yourself and the Mac (2) wear a
wrist strap (3) exercise great caution in removing the "dummy" PMMU
and (4) make sure the PMMU is seated all the way in its socket (it
does not go in easy - if you don't get it in your Mac won't boot!) -
be careful not to touch the pins or bend them when inserting the
PMMU. (If you know all of these cautions - my apologies; but I
think it is best to be safe when dealing with static sensitive
circuits).

Good luck with your installation.

Joseph Warden
Rensselaer Polytechnic Institute