# Serial Port Problems when running a net+50 at 33Mhz

**URL:** <https://forums.digi.com/t/serial-port-problems-when-running-a-net-50-at-33mhz/5210>\
**Category:** NET+OS\
**Created:** [May 27, 2003, 6:04pm UTC](https://forums.digi.com/t/serial-port-problems-when-running-a-net-50-at-33mhz/5210 "2003-05-27T18:04:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![system](https://us1.discourse-cdn.com/flex016/uploads/digi/original/1X/11da31a6a1fbcd03ef21d3f785c317c824009ae2.png) [@system](https://forums.digi.com/u/system)\
**Post date:** [May 27, 2003, 6:04pm UTC](https://forums.digi.com/t/serial-port-problems-when-running-a-net-50-at-33mhz/5210/1 "2003-05-27T18:04:32Z")

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We are trying to run a net+50 at 33Mhz and are having trouble with one of the serial ports. The reason we are running at the slower speed is because we had a bad board layout and the system/memory is unstable at 44Mhz because of it. we are using an external ttl oscillator. I changed the define XTAL1\_FREQUENCY to 33177600, and the define PLLTST\_SELECT to SELECT\_THE\_XTAL1\_INPUT. With the previous setup the following occurs. Serial port 1 used as a console at 9600 baud. This serial port works correctly. Measuring the baud rate on an oscilloscope shows error less than 0.2% Serial port 2 used to talk to a modem at 2400 baud. This serial port is off by 2.5% as measured by an oscilloscope. It makes no sense why the 9600 works and the 2400 does not. any help would be appreciated. I belive our net+50 version number is 24. -Blake

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**Author:** ![system](https://us1.discourse-cdn.com/flex016/uploads/digi/original/1X/11da31a6a1fbcd03ef21d3f785c317c824009ae2.png) [@system](https://forums.digi.com/u/system)\
**Post date:** [June 9, 2003, 3:24pm UTC](https://forums.digi.com/t/serial-port-problems-when-running-a-net-50-at-33mhz/5210/2 "2003-06-09T15:24:00Z")

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Are you using external crystal or oscilator ? does it work fine on 44Mhz (your board or Dev. Board) ? is it a problem of serial port 2 ? Have you tried 9600 on serial port 2 or 2400 on serial port 1 ? What kind of modem are you using ? Normaly it’s ok and even recommended to set the serial speed to the modem higher then the actual baud rate between modems.