Disconnecting the Serial Debugger?

[jnelson]

Hey All,

I posted this earlier in one of the other sections of the forum, but didn't get any responses. I'm currently working on a project on a development board based on an MC9S12 MCU using CodeWarrior and a serial connection between the board and the computer to load the code. The program runs perfectly when loaded onto the board, but once I disconnect the board from the serial cable connecting it to the computer, the board freaks out. It seems to be attempting to take input from the serial port, in spite of there not being anything attached. I'm fairly certain my code isn't telling it to pay any attention to the serial input, so I was wondering if anyone had any ideas why it's trying to take this serial input and how to make it stop.

-Jorgen

Message Edited by jnelson on 2008-11-04 08:52 PM

Message Edited by jnelson on 2008-11-04 08:52 PM

[Lundin]

It is impossible to answer the question since you don't tell us what serial bootloader you are using. "Serial connection" could be anything, though I assume you mean RS-232.

The best solution is to get a BDM pod. It loads the code 100 times faster and you won't get issues like this.

[jnelson]

I'm using Freescale's HCS12 Serial Monitor over an RS-232 connection.

Thanks for the response and sorry for being vague, I'm a huge noob at this, to tell the truth.

[kef]

Some RS232 level translators do have built in pullups/pulldowns. And some don't. Those without pull devices can float when disconnected, and make your MCU busy reacting to this noise. You could check that with scope. If TTL RX output to MCU oscilates or goes low instead of staying high, then you could try to pull nonTTL RX input to negative voltage level. If your chip is somewhat like MAX232, then >10k resistors between pin6 (V-) and one of (or both) nonTTL Rx inputs (pin13 or pin8) could fix that.