slowest practical baud rate?

Question

I'm trying to run a PIC12F675 with an external 32.768KHz crystal to maximize battery life.

I would like to interface to the part with a serial interface. I've tried

300 baud and 110 baud (no partiy, 8 data, 1 stop) but they didn't work. 300 baud gave invalid character returns and 110 baud didn't show anything. I'm interfacing with a HyperTerminal session. I have serial input going in to pin A3 (I declared NOMCLR in the fuses) and output going out of pin A2.

I can see the program running (as indicated by toggling of a heartbeat indicator) but the code does not recognize the serial input characters correctly.

Has anyone tried this "extreme" condition or am I just "spitting into the wind"? :)

Thanks.

Dave

Geo · Accepted Answer

Don't bother with hyperteminal - google for "bray terminal" - this lets you see precisely what is going on and allows you to control handshaking pins. I assume you are using a simple RS232 interface powered from the port?

Geo

starfire · Answer

Thanks for the response. I'll check into the "bray terminal".

Yes... I have a simple three-wire interface with a ICL3232 (MAX232 clone). I'm running the whole system on two AA cells (about 3.2VDC with a multimeter).

I have been trapping the log from the HyperTerminal session to a text file that I examine in hex after the fact. The characters (when I see them) don't look anything like what was sent.

Dave

TT_Man · Answer

SNIPNormal Max232's won't run reliably at 3.3 V, as I found out recently. 2 solutions- use a 2N7000  pulled to RST and set RST true ( works fine for me) or use a true 3.3 v compatible mrs232 chip......

starfire · Answer

The Intersil ICL3232 is rated to run from 3.0VDC to 5.5VDC, it only draws 1uA quiescent current, and it takes 0.1uF caps.I've never had a problem.   Good chip.Dave

Geo · Answer

You can see hex directly with "Terminal". You can also set parity data and stop bits BUT - I have just noticed that it lowest baud rate is 600... An alternative (on my desktop) might be TeraTerm Pro

formatting link

which does list 110 baud but I am not sure of its hex capabilities.

Geo

slowest practical baud rate?

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