I'm trying to use the Casio CE-515P plotter with my PC-E500S calculator and CE-130T RS-232 interface. I'm using a homemade cable which I triple-checked against the manual for correct connections. The plotter works fine when I use it connected to a parallel port on a PC but when I try to use it through its serial port, I get garbage. I've checked the OPEN statement on the calculator

OPEN"COM:1200,N.8.1" AS #1

and it seems to match the plotter's parameters.

My plotter's switch settings are SW-1 and SW-2 OFF, SW-3, SW-4, SW-5, SW-6 ON.

This should be 8 bits, RS-232C, CR/LF and RS-232C levels.

What might I be doing wrong?