Kenneth C. Fenney says:
I did a fair bit of work on this chip for a client just a few months ago... you are right to clear the overrun condition by clearing and then setting CREN which has the effect of resetting the receive logic-otherwise the hardware won't shift anymore bytes out of the receive shift register if OERR is set.
However, this bit has no effect on the framing error flag which is just a pronouncement that a stop bit wasn't detected when it should have been. This flag is set/cleared every time you read the receive register (RCREG), and it has no deleterious effect on the UART's behaviour - unlike the OERR bit which gums up the works until you reset it. It does mean that you should *save* the framing status immediately after a read, especially if you're running on rda interrupts and may want perform some out-of-band ack/nack or re-send logic.
As far as I can tell, this is the same for all the other PICs with onboard UARTs (well at least the 65, 73A, 74A, and 77) that I've worked with.
M. Adam Davis says:
- Check and initialize the several registers associated with the UART:TXSTA RCSTA SPBRG PIR1 PIE1 TRISC (TX & RX pins both input)
- Follow the suggested initialization order on the data sheet (p.107 and p.109 on the 17c74 datasheet)
- Do NOT use the baud rate tables in the data sheets, Use the calculations instead:Fosc/(64(spbrg+1)) BRGH = 0 Fosc/(16(spbrg+1)) BRGH = 1
(for instance the table for BRGH=1 at 4MHz async says 57.6kbps at spbrg=25, which is incorrect. 9600 is correct for spbrg=25 @ 4MHz. It /looks/ like the BRGH=1 tables are the only ones incorrect, but you should double-check)
- Make certian TRIS for RX and TX pins are BOTH input (counterintuitive, but necessary)
Thomas C. Sefranek's 16C73 USART Serial Port Gotcha List and Source
|file: /Techref/microchip/16xuarts.htm, 2KB, , updated: 2000/4/10 10:57, local time: 2021/12/3 20:31,
|©2021 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/16xuarts.htm"> microchip 16xuarts</A>
|Did you find what you needed?|
PICList 2021 contributors:
o List host: MIT, Site host massmind.org, Top posters @20211203 Neil, Harold Hallikainen, Alan Pearce, RussellMc, Bob Blick, Allen Mulvey, Justin Richards, Dwayne Reid, madscientistatlarge, Sean Breheny,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!