boot4p - TRS-80 Model 4P RS-232 downloader

boot4p takes a TRS-80 program in .cmd, .hex or .cas format and downloads it over RS-232 to a TRS-80 Model 4P.

A precompiled binary for Windows is included along with the source code. It has not been ported to MacOS or Linux. Should be a fairly simple matter of using the necessary files and APIs to access serial devices. These program loading routines are the same ones used in my TRS-80 emulator.

If run with no arguments boot4p will give a quick summary of the command line arguments, a list of available COM ports and possible baud rates.

Before downloading you'll need to connect your PC to the Model 4P with an RS-232 cable. I use a USB to serial converter and then a DB9 to DB25 converter. And also a null modem, if I recall correctly.

The 4P has a built-in RS-232 boot loader that boot4p talks to. To activate the boot loader hold down the right shift and BREAK keys together when powering on or resetting to 4P. You should see a "Not Ready" (or sometimes "Ready") prompt appear on the screen. Typically it will be "Not Ready" indicating the PC hasn't turned on DTR or some other signal line.

Once the two are connected run boot4p. Typically:

      boot4p -c 3 program.cmd
You should see the 4P say "Ready" on screen and then "Found Baud Rate". The program should download and execute in short order.

To give more flexibiity in what can be downloaded, boot4p first downloads a secondary bootstrap loader which downloads your file. It displays the current character on screen to give a little more feedback that progression is being made.

Option Reference

-c port#   
Use the given COM port (e.g., -c 3 for COM3)
-b baud-rate   
Download at the given baud rate (e.g., -b 9600)

boot4p is most generally of interest to programmers wanting to test their code. Unless some advanced utility is provided it cannot be used to download files onto diskettes or hard drives.

George Phillips, December 12, 2020. george -at-