89c668 ISP

[SU]

Hi,

     after two days troubleshooting and not changing any hardware, tonight it finally works. i still don't quite understand why.

     now the new problem is that every time i turn on the power supply for 8051 board and ISP interfacing board (2 max232 on it to hardware generate RST and PSEN), i can download the firmware twice; sometimes even cannot download once. it says " unable to access COM port. Ensure no other applications are using the device. try rising or lowering baud rate".

     however, without changing anything, i then turn off the power and after a while turn no again, i can download the firmware again.

     any suggestion is appreciated.

guodong
thanks

[erik malund]

>>max232 to  generate RST ...however, without changing anything, i then turn off the power and after a while turn no again, i can download the firmware again.<<

I have NEVER heard of the MAX232 as a reset generator.  The very symptoms you see should tell you to install a proper supervisor chip.

Erik

[Andy Ayre]

Do you have both P2.6 and P2.7 pulled high when resetting the device into ISP mode? Only pulling one of them high can lead to erratic results.