HP48GX RAM card design

[wan]

(01-18-2021 03:09 PM)Eric Rechlin Wrote:  The connector on the edge of my RAM cards is actually 2.0 mm thick, with the total card thickness being about 2.5 mm, so I would think a better approach would be to start with something approximately like what you did (a 0.6 mm board with the gold fingers flipped to the other side), and then add a second bare 1.2 mm board glued to the top, with holes for the components to go through it, to add thickness (for the edge connector) and provide some protection for the components on the board.

Yes, that's what I did. A bare 1.2 mm board on top is necessary. An optional short 0.6mm board on back can help(2.4mm total then), leaving goldfingers uncoverd. Pay attention to the location of the batteryholer to avoid scratching in card slot 2(no worry in slot 1). You can get a smooth insertion by this layout, even neither a handle nor a hole is needed for pulling out.

(01-18-2021 03:09 PM)Eric Rechlin Wrote:  Also, what was the reason for removing the pull-up resistors on WE and OE?

According to this post
https://www.hpmuseum.org/forum/thread-13070.html
Mfleming mentioned two pullups on OE/ and WE/, and at 47K they could sink tens of uA. So they are removed for power saving.
I think the 330 ohm series resistors for data lines can also be cancelled.

(01-18-2021 03:09 PM)Eric Rechlin Wrote:  Finally, might you be able to please share your modified layout?

The picture of the actual board is in the attatchment.