HP 48SX/GX display output for overhead projectors

[Chris Dreher]

I recently picked up an Invision 48, which was something you plugged into an HP 48SX/GX card slot for classroom overhead projection.
http://www.ebay.com/itm/Invision-48-HP-4...2451231150

I was wondering if anyone knew of detailed information of the card connector signals used for outputting the display. I've been able to find pinout information at http://www.hpcalc.org/hp48/docs/misc/cardpins.txt and general chip information at http://gecw.co.kr/ic/SED1181.pdf which lets me at least know what the upper clock speed limits are for XSCL.

However, what I don't know are:

• What's the actual clock rate of the XSCL pin?
• How many pixels are output on LD[0] and LD[1] between each LP pulse?
• What the allowed voltage ranges are (I have some guesses)?