Hi Andy

Thanks for your reply.

I have my program running in an endless while loop doing the printf with a delay function which I wrote.

I tried using the hello project and by itself compiles fine but when I add the default STARTUP.A51, the Keil compiler complains about:

Warning L1: UNRESOLVED EXTERNAL SYMBOL
SYMBOL: ?B_SWITCH0
MODULE: /STARTUP.OBJ (?C_STARTUP)

WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL ...etc

Do I have to change the STARTUP.A51 even for the hello world program?

Much thanks.

Thomas