Dynamic Engineering Portable PDS RAM Card

[David Cook]

I just bought a Dynamic Engineering Macintosh Portable RAM card with 2 MB of RAM installed.

I also purchased new old-stock Toshiba TC 518512FL-80 PSRAM chips to bring the card up to 8 megabytes. My plan is to use this on a 5120 (non-backlight) Portable.

The jumpers on the 2MB card are all installed except E1. I've seen a picture of this model of card with all the memory populated, where only jumper E3 is removed. So, that's what I intend to do.

Can anyone tell me (@techknight?) the jumper configurations? Is there anything I need to do with them to switch between a 5120 and a 5126? Is there a jumper to reduce memory to 7 MB on the card so that this can max out a 5126 but then be switched back to 8 MB to max out a 5120?

Thank you in advance,

David

 

[David Cook]

I have soldered on all the RAM. It works great in System 7.1 on a 5120 Portable. It shows 9MB total and passes all the memory test applications.

However, in System 6.0.8, it crashes when doing something as simple as displaying the About box in the Finder. I recall reading about a solution for this, but I can't seem to locate it on the forums. Does anyone remember?

 

[David Cook]

As a workaround, adding a >=1MB RAM disk in the Portable control panel seems to prevent crashing.

The error is a memory manager error. That's suggests a bug or limit in System 6 beyond 8 MB. I tried using System 6.0.8L without success. I wonder whether a Macintosh LC with > 8MB will crash. I'm going to try it.

 

[Garrett]

Great work! I saw this card on eBay as well - glad someone here snatched it up. Looks like the same RAM ICs that the PowerBook 1xx series uses. Did you have to tinker with the jumpers to get it working? I wonder why Dynamic Engineering didn't use the dedicated RAM expansion connector, but rather the PDS interface... access to more signals not present on the RAM slot?

 

[David Cook]

Did you have to tinker with the jumpers to get it working?

Yes. For 8 MB, I moved E3 to E1. So, all jumpers populated except E3. I will play with it further to figure out how to make it 7 MB for use in the 5126.

I wonder why Dynamic Engineering didn't use the dedicated RAM expansion connector, but rather the PDS interface

I believe the RAM slot is limited to 4 MB (recent recreations use an extra wire to provide more). Additionally, the system provides the refresh and data ready signals for the RAM slot. On the PDS slot, the card has complete control.

Macintosh LC with > 8MB will crash

I tested this. It does not crash. But, it does bump up the amount of memory consumed by the system to keep application memory <= 8MB in System 6. That is, even though the LC memory map places ROM such that 10 MB of contiguous memory is available in 24-bit mode, it still limits it to 8MB in System 6.