Upgrading Ports card to add memory

[Karl Swartz]

In article <13651 at cbnews.ATT.COM> mvadh at cbnews.ATT.COM (andrew.d.hay,54242,wi,1d007,508 374 5484) writes:
>In article <19876 at ditka.UUCP> kls at ditka.UUCP (Karl Swartz) writes:
>"If your card has sockets for the memory chips and the associated
>"control circuits all you have to do is populate the memory array
>"and change a couple of jumpers.  Otherwise, you're out of luck --
>"there are PALs and/or custom ICs in the control section that you
>"won't be able to get.
>
>not true!
>we've converted several ports-only boards here (using a
>ports-and-memory board as a guide) ... it's all standard
>ttl and discretes and a resistor pack or two.

Right you are!  My hardware knowledge goes little beyond that which
can be accomplished with a Phillips screwdriver (and sometimes not
even that far), so I was just repeating what I'd heard before.  But
since I just got a ports-only combo board I was curious to see just
what the strange chips are.  Low and behold, it was all stuff that
even I could recognize as being readily available.

With a bit of help from my EE housemate I believe I nailed down all
of the differences between the two boards:

ICs (note that rows are strangely designated: A, B, C, P, H, J, K)

   1  74AS74	(1B)
   2  74LS280	(2C, 2P)
   1  74F00	(2H)
   1  74F32	(2J)
   1  74F08	(3A)
   2  74F138	(3H, 3J)
   8  74F258	(3K, 4A, 4B, 4C, 4P, 4H, 4J, 4K)
   -  spare	(11J)
  54  41256-15	(columns 5 - 10, all nine rows)
	socket these; array need not be fully populated

Resistors

   2  33 ohm, 5%, 1/4 watt
		(R1, R2)
   -  remove	(R3, R8)
   1  10X-1-102	(RP1)
	replacement part
   1  10-1-560	(RP11)
	replacement part
  10  8X-2-330	(RP2, RP3, RP4, RP5, RP6, RP7, RP8, RP9, RP10, RP12)

Capacitors

   -  remove	(C18)
  29  0.01 mf	(C7, C19, C49, C50, C72, C96, C111,
		 C10, C24, C42, C52, C63, C74, C81, C99, C113,
		 C12, C26, C44, C54, C65, C76, C83, C101, C115,
		 C28, C56, C78, C103)
	same type as C5
  29  0.1 mf	(C71, C97,
		 C8, C23, C41, C51, C62, C73, C80, C98, C112,
		 C11, C25, C43, C53, C64, C75, C82, C100, C114,
		 C13, C27, C45, C55, C66, C77, C84, C102, C116)
	same type as C4

Jumpers

   3  2-pin Molex jumper blocks
		(W1, W2, W3)

Notes:

   1.	The boards that I compared (a 1.5 MB combo and a ports-only
	"combo") are Rev. E so all differences should be isolated to
	memory versus non-memory, but no guarantees.

   2.	Resistors R3, and R8, and capacitor C18 should be removed.

   3.	IC location 11J is not used.

   4.	Resistor packs RP1 and RP11 have differenet packages, but I
	couldn't discern any part numbers on the ports-only board,
	so they may in fact be electrically identical.

   5.	DRAMs can be 150ns parts, though when I checked today 120ns
	parts and even 100ns parts were actually cheaper than 150ns
	pieces.  No point in buying slow if they cost you more!

   6.	See my previous post or the "EIA/RAM COMBO BOARD Installation
	Guide" for proper settings of jumpers W1 - W3, and for which
	columns to populate if you want less than the full 1.5 MB.

   7.	Compare your board to one that already has memory if you can.
	I haven't upgraded one myself, I just compared my two boards
	and may have missed something.  (Use the information herein
	at your own risk.  Your mileage may vary.  Offer void where
	prohibited.  Unleaded fuel only, baby on board, and all that
	other drivel that makes the lawyers happy.  :-) )

-- 
Karl Swartz			 |UUCP	uunet!apple!zygot!ditka!kls
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