12F629 maximun Baudrate

[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

[MaxG]

Hello,
I have increassed the frec. of the crystal to 18.432 Mhz (I use this not very usual frec for generating accurate 4ms periodic interrupts) and put
DEFINE OSC 16
DEFINE HSER_TXSTA 20h
DEFINE HSER_BAUD 115200
in the testing software.
HSEROUT can output now 49 bytes in 3.340ms from inside a for..next loop (it counts an small time for jumping from the end to the begining of the for), what makes about 146Kbit/sec. The PIC used is a 16F876-20.

Ron, could you tell me what model have you pushed to 115200 baud with a 4Mhz crystal? I will try to reproduce your results. I do not like loosing time rediscovering the gun-podwer.

Last question: how can I define my 18,432Mhz oscillator to let PB generate accurate timming? Could it be done?

Thanks a lot
Maxi.

[Melanie]

>> Last question: how can I define my 18,432Mhz oscillator to let PB generate accurate timming? Could it be done?

No. If you want to use faster clock speeds with PBP keeping good order, pick a frequency that PBP supports - see PBP's manual.