Post by thread:20MHz clock problems

Hello PIC experts, I am developing a small project using the PIC 16C74 and recently needed to change the Crystal from 16MHz to 20MHz. When I did that, a problem started with the asynchronous communication controller, it started to recived wronge characters. Has any one had such problems ? Is 20MHz Crystal works OK with the 16C74 (the documentation says it should) ? Any special modification to the Crystal circut needs to be added for the 20MHz clock ? thanks chaipi \\\|/// \\ ~ ~ // ( @ @ ) ----------------------------oOOo-(_)-oOOo-------------------------------------- ! ! ! Chaipi Wijnbergen ! ! Electronics/Computer Eng. M.Sc. Tel : +972-8-9343079 ! ! Optical Imaging Laboratory Fax : +972-8-9344129 ! ! Brain Research Center Email : spam_OUTchaipiTakeThisOuTtohu0.weizmann.ac.il ! ! Weizmann Institute of Science URL : http://www.weizmann.ac.il/~chaipi ! ! Rehovot 76100 ISRAEL IPhone : chaipi ! ! ! ------------------------------------Oooo.-------------------------------------- .oooO ( ) ( ) ) / \ ( (_/ \_)

Chaipi Wijnbergen wrote, >I am developing a small project using the PIC 16C74 and recently >needed to change the Crystal from 16MHz to 20MHz. When I did >that, a problem started with the asynchronous communication >controller, it started to recived wronge characters. Check out pages 2-600-607 of the MC 1995/96 Databook. It's the section on the (SCI) module, which has a formula for baud rate error and information on the registers etc. Mike

Hi Mike and all other PIC experts, thank you for your mail, I forgot to say in my mail that I made sure to change the baud rate generation constants, I'm using 9600 bps and BRGH=1. I replaced the constant 103 with 129 which should give the same error of +0.16%. Any other suggestion ? thanks chaipi On Thu, 11 Apr 1996 .....mriendeauKILLspam@spam@vicr.com wrote: {Quote hidden}> Chaipi Wijnbergen wrote, > > >I am developing a small project using the PIC 16C74 and recently > >needed to change the Crystal from 16MHz to 20MHz. When I did > >that, a problem started with the asynchronous communication > >controller, it started to recived wronge characters. > > Check out pages 2-600-607 of the MC 1995/96 Databook. It's the > section on the (SCI) module, which has a formula for baud > rate error and information on the registers etc. > > Mike >

Chaipi Wijnbergen wrote: > > Hello PIC experts, > > I am developing a small project using the PIC 16C74 and recently needed > to change the Crystal from 16MHz to 20MHz. When I did that, a problem > started with the asynchronous communication controller, it started to > recived wronge characters. I have had similar problems. Two different systems (both based on the '74) with two different boards (this does not appear to be a board level problem) both running at 20MHz. These systems were driven by a PC that sent down a sequence of commands and the PIC based boards fed back status information so error handling in the PC program handled 'cleaning up' the communications errors. Spent quite a bit of time trying to figure out what was wrong and it appeared that the PICs were to blame. - John Miskimins

Is it a know bug that the 74's have problems with their asynchronous communication controllers at 20 Mhz? I am/was planning a project with the 74 that would use serial comm, should I look at a different PIC? Please let me know if you have experienced similar problems. I believe their is a new revison of the 74, does it have the same problems? Thanks, Ben Ben Wirz Check out My Home Page for Great Deals on Bulk Buy's Nitinol Wire, LMD 18200 H Bridge and 10 Mhz PIC 16C84 blw2KILLspamcec.wustl.edu http://cec.wustl.edu/~blw2/index.html On Sun, 14 Apr 1996, John Miskimins wrote: {Quote hidden}> Chaipi Wijnbergen wrote: > > > > Hello PIC experts, > > > > I am developing a small project using the PIC 16C74 and recently needed > > to change the Crystal from 16MHz to 20MHz. When I did that, a problem > > started with the asynchronous communication controller, it started to > > recived wronge characters. > > I have had similar problems. Two different systems (both based on the '74) > with two different > boards (this does not appear to be a board level problem) both running at 20MHz. > These systems > were driven by a PC that sent down a sequence of commands and the PIC based > boards fed back > status information so error handling in the PC program handled 'cleaning up' the > communications > errors. Spent quite a bit of time trying to figure out what was wrong and it > appeared that the > PICs were to blame. > > - John Miskimins >

I have used the 16C73 at 20 MHz and a transfer rate of 19200 and I havn= =B4t experienced any trouble with the asynchronous communication. I believe that it is basicly the same kernel as in the 74. Jonas Andersson Ben L Wirz wrote: >=20 > Is it a know bug that the 74's have problems with their a controllers= at 20 Mhz? I am/was planning a project with > the 74 that would use serial comm, should I look at a different PIC? > Please let me know if you have experienced similar problems. I belie= ve > their is a new revison of the 74, does it have the same problems? >=20 > Thanks, > Ben >=20 > > Chaipi Wijnbergen wrote: > > > > > > Hello PIC experts, > > > > > > I am developing a small project using the PIC 16C74 and recently = needed > > > to change the Crystal from 16MHz to 20MHz. When I did that, a pro= blem > > > started with the asynchronous communication controller, it starte= d to > > > recived wronge characters. > > > > I have had similar problems. Two different systems (both based o= n the '74) > > with two different > > boards (this does not appear to be a board level problem) both runn= ing at > 20MHz. > > These systems > > were driven by a PC that sent down a sequence of commands and the P= IC based > > boards fed back > > status information so error handling in the PC program handled 'cle= aning up' > the > > communications > > errors. Spent quite a bit of time trying to figure out what was wr= ong and it > > appeared that the > > PICs were to blame. > > > > - John Miskimins > >

On Sun, 14 Apr 1996, John Miskimins wrote: > Chaipi Wijnbergen wrote: > > > > Hello PIC experts, > > > > I am developing a small project using the PIC 16C74 and recently needed > > to change the Crystal from 16MHz to 20MHz. When I did that, a problem > > started with the asynchronous communication controller, it started to > > recived wronge characters. > > I have had similar problems. Two different systems (both based on the '74) > with two different > boards (this does not appear to be a board level problem) both running at 20MHz. > These systems > were driven by a PC that sent down a sequence of commands and the PIC based > boards fed back > status information so error handling in the PC program handled 'cleaning up' the > communications > errors. Spent quite a bit of time trying to figure out what was wrong and it > appeared that the > PICs were to blame. > > - John Miskimins > I have the same problem also and still cannot fix it, I think that it is a bug. -Newson