12F629 maximun Baudrate

[MaxG]

Hi people, using a 12F629 and programming

INCLUDE "modedefs.bas"
DEFINE CHAR_PACING 1 'THIS DOES NOTHING HERE...

'SET INPUTS AS DIGITAL
CMCON = %00111111

lazo:
serout2 0,32,["1234567890"] '(1)
pause 20
goto lazo

I can see the serial output on my oscilloscope's screen, going at about 19200 baud and repeating with pauses in between. Reading the manual I understand that to set the baud rate to, we can say, 50000 sps, I must program
1000000/50000 - 20 = 0, instead of 32 in the line (1). If I program a value under 12, I get the pin going from 0 to 5volts (Vcc) randomly and of course no serial signal. The piece is running at 4Mhz from its internal RC oscilator. I read that 12bits PIC does not support serout2 because of its limitations, but it works (PBP v2.46) untill 19200 baud. What I am doing wrong?

Thanks

[Ron Marcus]

There is a lot of info on serial comms on this site. Do a search. Next, if you are going to run over 1200 baud, you NEED a crystal or resonator. RC is just too squirrley. That being said, you can run DEBUG instead of serin, up to 115200 baud....But only with a crystal. Cheers...

Ron

[MaxG]

Hi,
I put a 12Mhz cristal to make run a 16F84A. Again, if I try to go faster than around 50K baud (I have got near 90Kbaud programming 57600 and making the PIC believe that its cristal was 3.5Mhz) I got the same rubish out the selected pin for serial output. It happens the same with 12F508, 12F629 and now 16F84A. Also, DEBUG seems to reach a higher baudrate than SEROUT2 on the same µ.

All these nonsenses are puzzling me. I routinely programm in assembler for 16F876-20 and send data through a twisted pair cable at about 1.125 Mbit/sec.

Has somebody push the commands SEROUT2 or DEBUG to the limits?

Thanks.
Maxi.

[Ron Marcus]

Hi,
I put a 12Mhz cristal to make run a 16F84A. Again, if I try to go faster than around 50K baud (I have got near 90Kbaud programming 57600 and making the PIC believe that its cristal was 3.5Mhz) I got the same rubish out the selected pin for serial output. It happens the same with 12F508, 12F629 and now 16F84A. Also, DEBUG seems to reach a higher baudrate than SEROUT2 on the same µ.

All these nonsenses are puzzling me. I routinely programm in assembler for 16F876-20 and send data through a twisted pair cable at about 1.125 Mbit/sec.

Has somebody push the commands SEROUT2 or DEBUG to the limits?

Thanks.
Maxi.

I'm sorry, I just don't understand what you're trying to do here. Debug will run to 115K baud. If you want faster, go hardware, or shiftin/ shiftout with a faster clock.

[MaxG]

Dear Ron,
I am sorry for my poor way of self-explaining. I am only trying to transmit some data (16 bytes bursts) at 115Kbaud using a 16F84A, PBP and the command DEBUG or SEROUT. I started doing some testings on 12F629, 12F508... with their internal 4Mhz RC oscillators and I could not go faster than about 30Kbaud. I follow your advise and put a Crystal, 12Mhz, on a 16F84A to make my testings.

It happens the same; PBP and PIC 16F84A can not go faster than about 80Kbaud, sometimes even slower. DEBUG can not be used with 16F84a and a 12Mhz EXTERNAL HS OSCILLATOR for reaching 115Kbaud. I suppose (I know) that in pieces with specific Hardware for Serial in/out, rates faster than 115Kbaud can be programmed but I would like to know why I can not reach 115Kb with the configuration noted above and where can be found a document with the limits for the commands DEBUG, SEROUT, SEROUT2. Again, I apologize for my short knowledge, and hope that you will be kind enough for taking a glance on my problem.

Sincerely,
Maxi.

[NavMicroSystems]

The higher the baudrate the faster and more accurate the clock has to be.

I doubt you can achieve reliable 115k with only 12MHz Clock speed.

Try a faster (and calibrated) clock.

If you have a DSO, scope the output and push it step by step to the limits.

AND: I wouldn't put anything into production that is ways off specs.

[Ron Marcus]

I've had no issues with a 4 MHz xtal and Debug pushing 115200 baud. Am I doing something wrong(right)?

Ron