MAIL 232 Terminal Emulator

After fitting the serial interface CPS256 I used the JOYCE program MAIL232 as a terminal emulator. I liked the menu control very much and the program was very good for reading mail boxes at that time, also called Bulletin Board System (BBS) 1.

One day I invoked the program selecting a Baud rate of 300 Bd and I established a connection. After reading a few news I wanted to upload a file. I had to search for it stopping MAIL232 but without breaking the connection.

After invoking MAIL232 again I did not get contact although the modem indicated an established connection. Playing around I found out that the default Baud rate of 9600 Bd was selected!

An XBIOS routine for determining the current Baud rate does exist. But the rate of 9600 Bd was hard-wired in MAIL232 .

Analyzing the program using a debugger I found
  1. a table the Baud value was stored into,
  2. a CALL xxxx instruction at the beginning of MAIL232.
Here it was adequate for a patch that
  1. reads the Baud rate and stores it into the corresponding table,
  2. changes the CALL address to a new routine directly behind MAIL232.
After inputting the patch the connection stays intact interrupting MAIL232. But the menu still displayed the default Baud rate of 9600 Bd. A second analysis showed another table entry which was not synchronized with the first one.

Adding some more code leaded to the result as requested.

Find the patch for MAIL232.COM version 1.2 here. Maybe the code must be adjusted for other versions. After assembling the code must be installed. A good program for doing that is MLOAD.COM. For the sake of completeness find the disassembled version of MAIL232.COM here.
1. File transfer protocols such as XMODEM or KERMIT are more popular. Find here a description of the protocol used by MAIL232: Intelligent File Transfer protocol (The program describeb there was also published in the German Schneider CPS8256 Benutzerhandbuch, here as HEX dump. Both programs differ slightly at one point, find the common source here)