The Kriz tablet definitely existed, I have half of one
(it's the "mouse"
portion, it basically looks like a Hawley mouse without the ball). The
device is supported in the Z80 code, PERQ microcode and POS software.
Are you thinking of the PERQ 2 version that had a synchronous serial interface? That
certainly exists (in both landscape and portrait versions)?
The PERQ1 one looks odd... I seem to remember something about analogue
signals on the interface connector.
-tony