Serial port settings for given crystal

[Scampy]

Just need some guidance on setting up the defines for serial communications when using a particular crystal.

I'm using a 20 mhz crystal.

Here are my config settings

ASM 
  __CONFIG    _CONFIG1H, _OSC_HS_1H
  __CONFIG    _CONFIG2L, _PWRT_ON_2L  
  __CONFIG    _CONFIG2H, _WDT_ON_2H & _WDTPS_512_2H
  __CONFIG    _CONFIG3H, _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H  
  __CONFIG    _CONFIG4L, _LVP_OFF_4L & _XINST_OFF_4L
ENDASM

I've cut and pasted code from a previous project but that won't allow connection with the port.

DEFINE HSER_BAUD    115200        ' Hser baud rate 
DEFINE HSER_RCSTA   90h           ' Hser receive status init 
DEFINE HSER_TXSTA   20h           ' Hser transmit status init 
DEFINE HSER_CLROERR 1             ' Hser clear overflow automatically 
DEFINE HSER_SPBRG 25  ' 115200 Baud @ 40MHz, -0.22%
SPBRGH = 0
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
ColumnWidth CON 10

I've tried changing the baud rate to 9600, and different values for SPBRG as I'm not running the PIC at 40Mhz...

Any help would be appreciated

Malcolm

[Demon]

Off the top of my head, you have 115200 Baud @ 40MHz with 20MHz crystal.

Robert

Edit: Have you tried Steve's baud rate calculator tool?

http://www.picbasic.co.uk/forum/showthread.php?t=4994

[Scampy]

Robert, many thanks for the link.

I've entered the parameters for 9600 baud, with a osc of 20 and get the resulting code

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 8   ' 9600 Baud @ SPBRGH = 2
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
RCSTA = $90   ' Enable serial port & continuous receive
TXSTA = $24   ' Enable transmit, BRGH = 1
SPBRG = 8     ' 9600 Baud @ -0.03%
SPBRGH = 2

However I still get an "unable to open comport" message when using the serial comm tool in Microcode studio..

I'm using a USB to 5v TTL serial cable that is based on a prolific chipset, and to test this I loaded up an example code I had from a previous project, which relied on a different crystal (12 mhz) and then used the PPL multiplier to up the OSC to 48. This code simply echoed what is sent via the TX box and worked fine, so the physical communication between PC and PIC is fine. The only drawback of using the 12mhz xtal and the OSC48 is that the LCD, and temp sensor comms are screwed. I really need the serial coms to work with a OSC of 20 and a 20mhz xtal as the rest of the code (temp sensor, RTC etc ) all work fine at these settings.

Any ideas ?

[HenrikOlsson]

Hi,
The fact that the PC can't open the COM-port has absolutely nothing to do with the code in PIC.

The problem is with the USB dongle, its drivers, the USB port or the PC. Plug the dongle into your USB-port, open the device manager and check which COM-port number Windows has assigned to the dongle. Then make sure you select that COM-port in the Serial Communicator.

Another possible cause for not being able to open the port is that it's already opened, perhaps by another program or possibly that some program didn't close it properly. Try restarting the computer.

/Henrik.

[Scampy]

Thanks for the suggestions, but as I said I can load one HEX file, place a 12mHz xtal in the development board and click on connect in the serial tool and it works fine. Disconnect the port, load up the other code, replace the 12mhz xtal with a 20 mhz with identical port setting in the serial tool (and those that match the settings in the code) click on connect and get the "unable to open com port" type message.

Settings in device manager mimic those set in the code. No issue reported, driver provided by MS

[HenrikOlsson]

That really doesn't sound right. In fact, you should be able to open the port (ie click connect in Serial Communicator) without having anything what so ever connected to the dongle. And you should still be able to open the port even if the baudrate in your PIC program is different from the one you setup in Serial Communicator - it won't work of course but you should still be able to open the port.

But OK, if that is the case I'm afraid I don't have the faintest idea what's going on :-(

/Henrik.

[Scampy]

Moral of this story... don't rely on cheap crap from china...

I have a sparkfun breakout board that's based around an FTDI chip - used this and was able to communicate 1st time........

[Demon]

Good, I'm going to take credit for solving this. lol

(just woke up)

Robert