🚀 go-pugleaf

In article <4Q85RLAMZi3yEwP5@amigo.demon.co.uk>, David Mahon
<dmahon@amigo.demon.co.uk> writes
>In article <853149508snz@longley.demon.co.uk>, David Longley
><David@longley.demon.co.uk> writes
>>I  have an HP Laserjet 5. I'm about to put a JET DIRECT card  in. 
>>Card is a J2552 UTP/BNC (someone said I needed a HPJ2382A 10baseT)
>>The network used twisted pair 10-base-T.
>>
>>Is there anything else to it apart form plugging in the card?  Is 
>>the  above the right card? Do I need to upgrade the RAM  (it  has 
>>4MB)  now I am putting in a JET DIRECT card? If so, will  normal, 
>>non-parity 72 pin SIMMs do? Do I have to add RAM in pairs?
>
>I believe it uses non-parity 72 pin SIMMs, like my HP Laserjet 6P.
>
>The RAM needs to have presence detect enabled. It needs to be 70ns.
>
>If you can't get such a chip cheaply, just buy a regular 72pin non-
>parity SIMM without presence detect, and, using conductive paint and a
>regular fine brush, connect the relevent jumpers yourself (you'll need
>to paint between one and three connections, each about 2mm long - very
>non-technical).
>
>I used a 4MB $15 SIMM in my HP 6P - works fine. HP charges about $150
>for the same thing.
>
>Information on presence detect can be had by using Alta vista, and
>searching for "presence detect" (including quotes).

The logic behind this is interesting - Presence Detect (PD) is based on
4 or 5 pins out of the 72 (5 if its ECC memory). This gives only 16
combinations of non-ecc memory, of which one is all pins open (NC). The
all PDs NC combination is indistinguishable from not having any PD at
all, and it just so happens that all PDs NC is a 2M x 32/36/40, 60ns
option, thus in order to use a SIMM with PD, and to able to detect that
PD is actually there, you cannot use 60ns memory. Amazing, huh?

So, watch out - many companies (Simply are an example) only supply 60ns
SIMMs, but mark them as 70 when people ask for 70ns SIMMs. Just look at
the actual chips, and you will see the speed digit at the end of the
chip part number (e.g. xxx-6 or xxxxJ6 etc.).

The best page I know of about PD is from IBM, I don't have the URL handy
but the page comes up under AltaVista as "72 Pin SIMM Characteristics"
and it has a section on "Presence Detect Considerations".

Yes, you can fake a non-PD SIMM if you are careful, but, David
(Longley), I would think really carefully about doing it yourself, given
your past experiences ;-)

HTH,
-- 
Nick de Smith