Alternate RAM

[Dan K]

Doggone limit on message length! This is the third time I'm posting this, 
only this time without the quoted stuff.

I've come to the conclusion (based on all reports) that a "standard" 3.3v 
EDO SODIMM will _NOT_ work in a 2400 without some modification. Whether 
that mod is trivial, and therefore actually _do-able_, or not is the 
question now.

I'm not sure, but what it looks like to me is that perhaps a pair of 
address lines need to be swapped on a standard sodimm to allow use in a 
2400. Possibly. Maybe. : >)

". . . the connections to device address bits 9 and 10 must be swapped on 
the DIMM."

What that exactly means, heck if I know. Swapped compared to . . . ?

A "standard JEDEC SO-DIMM" _may_(?) just describe the mechanical spec and 
not the electrical spec. As I have no idea what a "standard" 3.3v EDO 
SODIMM's electrical specs are, anyone out there knowledgable enough to 
compare that with the 2400's requirements? (see below)

Dan K (ignernt az dawg spyt n prowd uv it!)

------------------------------------------------------------------------
>From the "Delta Guide to the PowerBook 2400c Computer" devnote

<http://developer.apple.com/techpubs/hardware/Developer_Notes/Macintosh_CPU
s-PPC_Portable/PowerBook_2400c.pdf>

RAM Expansion

The PowerBook 2400c computer accommodates one SO (small outline) DIMM for 
RAM expansion. The DIMM can have either 16 or 32 MB of additional RAM.

The mechanical characteristics of the RAM expansion DIMM are given in the 
JEDEC speciÞcation for the 144-pin 8-byte DRAM SO DIMM. The PowerBook 
2400c computer can accommodate an SO DIMM with a height of 1.0, 1.25, or 
1.5 inches. While the JEDEC speciÞcation for the SO DIMM deÞnes a Serial 
Presence Detect (SPD) feature that contains the attributes of the module, 
the Macintosh PowerBook 2400c computer does not support the SPD feature. 
The computer requires the DIMM to contain EDO DRAM devices with access 
times of 60 ns or less.

The electrical characteristics of the DIMM must be the same as those of 
the RAM expansion module for the PowerBook 3400 computer, as described in 
the PowerBook 3400 Developer Note. To obtain that developer note, please 
refer to ³Supplemental Reference Documents² on page vii. 

IMPORTANT - Unlike the RAM expansion module for the PowerBook 3400 
computer, the SO DIMM for the PowerBook 2400c computer does not require 
an address buffer.

The PowerBook 2400c computer can accept a DIMM that uses 64-megabit DRAM 
devices. The electrical characteristics of such a DIMM must be the same 
as those of the corresponding expansion module for the PowerBook 3400 
computer: the DRAM devices must be 4 M by 16-bit devices with 12-by-10 
address multiplexing, and the connections to device address bits 9 and 10 
must be swapped on the DIMM.
------------------------------------------------------------------------
>From the "Macintosh PowerBook 3400 Computer" devnote

<http://developer.apple.com/techpubs/hardware/Developer_Notes/Macintosh_CPU
s-PPC_Portable/PowerBook_3400.pdf>

Table 4-13 {lists the types of DRAM devices possible, along with the pin 
assignments}
Type of DRAM device
512K by 8; 10 row bits, 9 column bits
2M by 8; 12 row bits, 9 column bits
1M by 4 or 1M by 16; 10 row bits, 10 column bits
2M by 8; 11 row bits, 10 column bits
4M by 1 or 4M by 4; 11 row bits, 11 column bits
4 M by 16; 12 row bits, 10 column bits

RAM Banks
The RAM expansion card can have up to four banks of RAM. Banks can be 4 
MB, 8 MB, 16 MB, or 32 MB in size. 

DRAM Device Requirements
The DRAM devices used in a RAM expansion card must meet the following 
minimum speciÞcations:
* Power supply voltage: 3.3 V 
* Access type: EDO
* Access time: 60 ns or shorter access time 
* Refresh: CBR, extended refresh capable (L-type)
* Refresh cycle: 15.6 ms 

RAM Expansion Card Electrical Limits
The RAM expansion card must not exceed the following maximum current 
limits on the +3 V supply:
* Active 500 mA 
* Standby 24 mA
* Sleep 12 mA 
During system sleep at the 15.6 µs refresh rate, the current for the 
entire RAM card must not exceed 12 mA. Vendors of cards that exceed the 
refresh-current restriction will be required to state in their user 
manuals that their cards may reduce the amount of time the computer can 
remain in sleep mode before running down the battery.

The capacitive loading on the signal lines must not exceed the following 
limits:
* DATA(0­63): 50 pF 
* RADDR(0­11): 140 pF
* /RAMWE: 140 pF 
* RAMOE: 140 pF 
* /RAS(n): 80 pF 
* /CAS(n): 50 pF