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Re: LF: Re: [rsgb_lf_group] Fast Serial Interfacing with PICs

from [Andy Talbot] [Permanent Link][Original]
To: [email protected]
Subject: Re: LF: Re: [rsgb_lf_group] Fast Serial Interfacing with PICs
From: Andy Talbot <[email protected]>
Date: Thu, 7 Apr 2016 22:07:26 +0100
Cc: [email protected]
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The pointer I had came from Johan who listed the PIC code  to get 3MBaud from the PIC's EUSART.    And I've just been trying this on a 16F688 only to find the PIC itself is doing something odd and sending multiple characters.  Each character is being send 4 or 5 times and that is certainly due to its internal misbehaving.   Further investigation is needed there.

The USB / FTDI interface works perfectly at 3Mbaud.  I proved this by connecting two PCs together via FTDI232  COM ports and writing software to communicate at full speed;  no problems there

Andy  G4JNT

On 7 April 2016 at 21:49, Wolfgang Büscher <[email protected]> wrote:
Hi Andy,

It was me, using a PIC16F1783 with 1 MBaud on an FTDI-based interface.
At higher bitrates, there were occasionally lost samples depending on the CPU load of the PC. So it wasn't a problem with the PIC, and not a problem with the hardware, but most likely a problem with the USB driver.

All the best,
   Wolf DL4YHF .

Am 07.04.2016 um 12:09 schrieb Andy Talbot [email protected] [rsgb_lf_group]:


I know the subject is nothing to do with LF, but I didn't keep the original thread...

A few months ago someone on one of these two LF reflectors pointed me at the Enhanced USART in the 16F688 and later PIC devices, saying how the baud rate could be set as high as Fosc / 4. So getting 3M Baud with a 12MHz Xtal for compatibility with FTDI chip COM ports at thier highest setting.

Who was it and have you managed to do this?   I finally got round to testing a 16F688 at 3Meg   and am getting some funny results that mean sometimes the PIC's EUSART sends the right data, and sometimes it gets itself tied up in knots, sending one character several times

It is not a programming error either, as the code works perfectly at lower baud rates, by just changing the divider.   The nature of the problem looks and feels like something inherent to the internals of the chip 

Andy  G4JNT



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Posted by: Andy Talbot <[email protected]>



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