While I am not familiar with the Z88, here is what appeared in ZQA!, Winter 93. It should work with the Z88 as it did with the PC.
It has been a challenge to have a 2068 communicate directly via modem with a PC modem to transfer text files. The procedure was to upload files to a BBS by one computer and then download with the other, until Bob Swoger spent an evening with me to tackle this problem.
To communicate, modems have to have a line that has a tone “carrier” and provides a ring “signal”. Connecting two modems together from two computers eliminates the carrier and the signal and the modems will not turn on. It has been done with the two modems connected to the same phone line. That held up calling or receiving phone calls for the duration, at 18 text characters per second which is what I got with the 2050 modem.
With a Hayes compatible PC modem, here is how:
1. Connect the two modem lines that normally go to the telephone line together using a two-line plug without any connections to the telephone line.
2. Turn on both modems and load the modems software. MTERM II (Loader V) or MaxCom Xmodem for the 2068. Load buffer etc. I used MaxCom.
3. Set both computers to TERMINAL mode and the TS-2068 to ASCII (toggle con: none). All other parameters have to match the PC modem’s of course or vice versa.
The following has to be done rather rapidly before the PC abandons the connections.
4. On the PC modem, ENTER ATA (which is Hayes command that forces the PC modem to answer the phone without the benefit of a ring or a tone). The PC modem emanates a long squeal and recognizes the signal from the other modem and CONNECTs.
5. Set the PC in RECEIVE mode, Xmodem 300 BAUD and enter the file name.
6. From the TS-2068 select SEND (transmit) file ‘name.Cm” and ENTER.
7. The PC acknowledges and receives the file.
8. Exit SEND to TERMINAL mode and ENTER Ctl Z (SHIFT-7 Z) to tell the PC “end-of-file”.