C251: RISM for USB Crashes at Startup

Information in this article applies to:

• C251 Version 1

QUESTION

I am using the C251 Compiler, USB, and the RISM monitor. I wrote a C program to locate the code to start at 4000h. After I load my program, it crashes and will not get past the startup code. I receive error messages like "lost serial transmission error". What is wrong?

ANSWER

The RISM monitor uses internal data memory to store its own variables. However, the first thing the startup code does is clear internal memory. This crashes the RISM monitor.

To fix this problem, include the startup code (START251.A51) in your project and set the EDATA length to zero. This change avoids clearing memory and allows the RISM monitor to run. However, your uninitialized variables will not be set to zero.

Be sure to check the Keil USB web page at http://www.keil.com/usb/ for more information about USB.

Last Reviewed: Thursday, February 25, 2021