Attempt to recieve values from the TI-66 printer port

[tryt]

Hello, it is me again.

Recently I have become interested in TI's programmable calculators, particularly the LCD models TI-55 III, TI-57 II, TI-60, TI-62, TI-65, TI-66, although I only have got my hands on a TI-65 and TI-66. Anyway, I enjoy writing programs and all, but one feature of the TI-66 has caught my interest: the two-pin printer port. This calculator from 1984 is compatible with the PC-200 printer from the same year. I cannot find one of these and the paper must be expensive to supply. I would like to create my own device to act as a "printer" and using a computer, record the outputs of the calculator for later use.

The calculator has three main printer uses, aside from a few others accessible with OP codes. First is the Print command, which prints the number in the display. Second is Trace, which prints the operations used during operation of the calculator. Third is the List command, which prints the program steps for debugging purposes. I have an oscilloscope and an Arduino kit to use to make my device. I have set them up to detect and save the output pulses from the calculator. However, whenever I print a value or use an operation in the trace mode, only a single or maybe two pulses are sent out, at a little over 3 volts.

From this I assume the information cannot be carried in this single pulse. The calculator must want a response from the "printer" in order to give me the rest of the data in pulses. However, after writing a simple program to respond, a single, double, or triple pulse in response at the same voltage with a few different time scales have returned no additional output from the calculator. I know that the calculator is recieving the response from my device because with one of the multi-pulse outputs, such as the = key in the trace mode, any signal I send between the pulses will delay the calculator's second pulse to later.

Is there some typical "handshake" signal used around this time which the TI-66 is expecting before it sends the actual data to print? Any information to help me is appreciated, and any clarifying questions I am open to answer.

Thanks,
tryt