View Full Version : CP/M, and BBSes via parallel modem? Please help

September 14th, 2017, 01:08 PM
Hi and thank You for answering, if You can do it.

I am looking for software - like Xmodem etc. that will allow me to connect to BBS via parallel (not serial). The project is inspired by seeing Altair 8080 browsing the Internet via Lynx on BBS.

Why parallel (or "Printer", literally port on computer) - because I don't have serial in my computer, and is not for e.g. S-100 or ISA system, with many expansion cards.

The computer - Polish Elwro 800 Junior (English, quite detailed info there http://oldcomputer.info/8bit/elwro800/index.htm ), basically Z80 similar processor(probably in most computers are U880). Operating system CP/J which is a CP/M 2.2 compatible, 64 KB of RAM(of course little less after loading system from floppy). Also if I can get a binary version of program I can probably easily put it on diskettes - e.g. using floppy editor of that computer format, and for example Rawrite for making it.

I still don't have a parallel modem. However I see three possible options. Plipbox(which I have) - Amiga parallel Ethernet card(probably won't work). Buying an centronics to serial converter, and using serial modem(will it work, maybe You known and used something similar?). Or just buying and finding parallel modems, despite being quite rare there is a possibility? Just read some articles about quite modern parallel modems used even to browse Internet with 56k.

September 14th, 2017, 10:22 PM
All the parallel port modems I know of needed special drivers to pretend to be a serial modem. Reinventing that would be a lot of work.

Ethernet: http://susowa.homeftp.net/index.php/kcnet-75/z80-tcpip-159.html and following pages has a good explanation of what is needed to support it. Also very complex.

I think a relatively easier path would be to remove the network connectors since those are useless. Then wire up a RS-232 serial port to the 8251 UART that used to handle the network. Still would require some effort designing interface code and adapting it to a poorly documented system but there is a lot of example Z-80 and CP/M code that accesses serial ports.

September 15th, 2017, 10:38 AM
Is your parallel port bidirectional?

September 15th, 2017, 11:47 AM
Yes; see Schematic (https://305f9ca0-a-62cb3a1a-s-sites.googlegroups.com/site/krzkomar/elwro-800-junior/junior_b.png?attachauth=ANoY7crtgYjZT132dRz6mQRLAJ VAgWJH1ZlWj-1XOOA6NAdT_fvtKXx2dw4PCiEbZgvbv06HqsFaGNyjgwfPjUlU Xtph_te5KrMMwNzqELG80shlTKFBKbvhxonO_sDqooU2K8Ylqq 9ZNkckWmliuv-RnnqaVfzRhsJreOZxAakcrJ0_VSpjej2TbR64lfMZfXUG5GU22 h7Bg_u3QopiDwAwX1NU7ch6F1zbIOCGi_1B390fC8x8KjI%3D&attredirects=0). Basically, the parallel port is hooked to 8255 port B for data and C for control. All 8 bits of port A are also available on a separate DE-9.

September 15th, 2017, 12:27 PM
You may want to try contacting the owner of https://elwro800junior.pl/elwro-804-junior-000007/ which describes a revised model that replaces JUNET with RS-232 (and other changes). The schematics, ROM, and software from that might simplify developing a similar modification on the 800.