HP 39gs and SD card

[rcpdvc]

HP 39gs has same PCB with SD socket footprint as a 50g. So, it is possible to mount socket and some components to get SD on 39gs. Of course, native firmware is not intended to work with SD, but it's implemented in newrpl (thanks to Claudio L.). Another advantage of SD is 50g-way flashing without Windows machine (real or virtual. Wine can be used to pass data over tty-COM, but flashing requires connection over USB driver).

To perform update save firmware file and "update.scp" text file containing firmware filename in card's root. Enter bootloader as usual (reset while holding "+" and "-"). Press "1" key ("1.UPDATE CODE"). Press "8" key (there is no hint for this on the screen, only "1.USB").

Missing resistors parameters are taken from 50g PCB photo, all in 0603 smd package.

PCB Nets Value Package
mark Ohm(F) mark

R61 7.DAT0 - Vcc 10k 103
R62 8.DAT1 - Vcc 10k 103
R63 9.DAT2 - Vcc 10k 103
R64 1.DAT3 - Vcc 10k 103
R65 5.CLK - CPU 10 100
R66 sw COM - Vcc 1k 102
R67 sw #WP - GND 100k 104 WriteEnable.
R68 sw CD - GND 100k 104
R69 2.CMD - Vcc 10k 103
C73 4.Vcc - GND ~0.1u - Decoupling. Accurate value not required.
C74 5.CLK - GND <10p -

I have omitted C74 at all. What the purpose of increasing CLK line capacitance? Noise filtering? Anyway it should be small enough to fit specification limits for total line capacitance (<40pF).
Confirmed working in bootloader (SD, MMC fat16 and fat32) and newrpl (SD fat16 and fat32).