Post by thread:transmission code

> Hi all.. > > I'am programming MIcrochip PIC16C73 and have problems with data > transmission using USART registers?. First, I enable Tx,Rx pines with SPEN > at RCSTA, then set TXSTA for async mode finally BRG register. When I send > a character it looks like there is no transmission. > > Some suggestions please? > > Thanks!! Here's some cut-and-paste from a little project I finished recently. Maybe it will help... <cut> ;+++ Initialize ports clrf PORTB ; Set all outputs low for now clrf PORTC BANK1 ; Define i/o port direction movlw B'11010000' ; SDI and RX/TX are inputs (really!) movwf TRISC ; for port C. movlw B'00000000' ; All pins are outputs movwf TRISB ; for port B. movwf ADCON1 ; Enable AN0-AN4 with Vref=Vdd movlw 0xff ; All pins are inputs movwf TRISA ; for port A. BANK0 <cut> ;+++ Start SCI BANK1 movlw D'25' ; 9600 baud movwf SPBRG movlw B'00100110' ; Asnyc, 8 bit, TX on, hi speed movwf TXSTA BANK0 movlw B'10010000' ; Enable UART and receiver movwf RCSTA <cut> SCI_CHAR_OUT: ; Send an ascii character out theSCI ; Enter with char to be sent in W SCI_DL: btfss PIR1,TXIF ; Is TXREG ready? goto SCI_DL ; No, wait movwf TXREG ; Yes, send the character return ; Done.

I know posting code is a no-no, but... My boss was having trouble using the USART on the 16C74. I spent 15 minutes or so changing the order in which the registers were configured until it worked. i'm not saying this is the only way (or the right way) to do it, but it works. Note that the comments are not mine and are quite ugly. Regards, Vincent Deno ;------------------------------------------------------------------------------- ----------------- Setup_UARTS setb RP0 ; setb INTCON.6 ; interrupt control clrb TXSTA.2 ; set BRGH mov SPBRG,#129 ; set baud to 2400 clrb TXSTA.4 ; clear sync clrb RP0 ; setb RCSTA.7 ; set spen setb RP0 ; setb PIE1.5 ; set rcie clrb RP0 ; clrb RCSTA.6 ; clear rx9 setb RP0 ; clrb TXSTA.6 ; clear tx9 setb TXEN ; enable transmission clrb RP0 ; setb RCSTA.4 ; enable reception cren setb INTCON.7 ; set gie ret ; return in bank 0 ;------------------------------------------------------------------------------- ------------------- > Hi all.. > > I'am programming MIcrochip PIC16C73 and have problems with data transmission > using USART registers?. > First, I enable Tx,Rx pines with SPEN at RCSTA, > then set TXSTA for async mode > finally BRG register. When I send a character it looks like there is no transm ission. > > Some suggestions please? > > Thanks!! > -------------- Vincent Deno Design Engineer Theta Digital Corp. http://www.thetadigital.com spam_OUTdenovjTakeThisOuTemail.uc.edu _____________ | ____ ____ | |/| | | | | |\| | | |/| |\| | | | | | | | | | | | |_/ | | \_| | | | | | | | |_/ /___\ \_|

Configure the Tx pin of Port C as output. Pailoor Carlos Fiestas wrote: {Quote hidden}> Hi all.. > > I'am programming MIcrochip PIC16C73 and have problems with data transmission > using USART registers?. > First, I enable Tx,Rx pines with SPEN at RCSTA, > then set TXSTA for async mode > finally BRG register. When I send a character it looks like there is no transmission. > > Some suggestions please? > > Thanks!! -- ------------------------------------------------------------------------ Chip Technologies - Microchip Design Consultant No. 70, 9th Main Road, Mathikere, Bangalore - 560 054. INDIA Tel : +91-80-3362807, Fax : +91-80-3369451 Email : .....chiptechKILLspam@spam@vsnl.com, Webpage : http://business.vsnl.com/chiptech ( Updated on 16th February ) ------------------------------------------------------------------------

At 12:09 PM 2/27/99 -0800, you wrote: >On Sat, 27 Feb 1999, Ravi Pailoor wrote: > >> Configure the Tx pin of Port C as output. > >NO! The UART will not work if the pin is set as output. GONG! It does work. All the programs I have use a 0 in the TRIS bit for the tx pin. Andy \-----------------/ \ /---\ / \ | | / Andy Kunz \ /---\ / Montana Design /---------+ +---------\ http://www.montanadesign.com | / |----|___|----| \ | \/___| * |___\/ Go fast, turn right, and keep the wet side down!

On Sat, 27 Feb 1999, Andy Kunz wrote: > At 12:09 PM 2/27/99 -0800, you wrote: > >On Sat, 27 Feb 1999, Ravi Pailoor wrote: > > > >> Configure the Tx pin of Port C as output. > > > >NO! The UART will not work if the pin is set as output. > > GONG! It does work. All the programs I have use a 0 in the TRIS bit for > the tx pin. On which chip? Let me quote from the 16C7x data sheet: ------------------------------------------------- Bit SPEN (RCSTA<7>), and bits TRISC<7:6>, have to be set in order to configure pins RC6/TX/CK and RC7/RX/DT for the Serial Communication Interface. ------------------------------------------------- Notice it says "set" not "clear". I was bitten by this the first time I tried to transmit on a 16C74A, so I remember it quite well - I have no idea how you made it work the other way, but "it works for me the way the book says" :-) Cheers, Bob

Bob Blick wrote: > On Sat, 27 Feb 1999, Andy Kunz wrote: > > At 12:09 PM 2/27/99 -0800, you wrote: > > >On Sat, 27 Feb 1999, Ravi Pailoor wrote: > > > > > >> Configure the Tx pin of Port C as output. > > > > > >NO! The UART will not work if the pin is set as output. > > > > GONG! It does work. All the programs I have use a 0 in the TRIS bit for > > the tx pin. > > On which chip? Let me quote from the 16C7x data sheet: > ------------------------------------------------- > Bit SPEN (RCSTA<7>), and bits TRISC<7:6>, have to > be set in order to configure pins RC6/TX/CK and > RC7/RX/DT for the Serial Communication Interface. > ------------------------------------------------- > Notice it says "set" not "clear". Does SET mean set the port bit as output ? The documentation is / may not clear in defining the state the Tx port pin that has to be "set". Pailoor

At 16:19 02/28/99 +0530, Ravi Pailoor wrote: >Bob Blick wrote: >> On which chip? Let me quote from the 16C7x data sheet: >> ------------------------------------------------- >> Bit SPEN (RCSTA<7>), and bits TRISC<7:6>, have to >> be set in order to configure pins RC6/TX/CK and >> RC7/RX/DT for the Serial Communication Interface. >> ------------------------------------------------- >> Notice it says "set" not "clear". > >Does SET mean set the port bit as output ? > >The documentation is / may not clear in defining the state the Tx port >pin that has to be "set". no, it is quite clear: it says the bits 6 and 7 of the TRISC register have to be set, which means the ports would be configured for input (ie. the output driver would be disabled), if they were just plain ports. if you have a look at the "portc block diagram (peripheral output override)" of a data sheet, you see the "peripheral oe" output enable, this is the one that switches the port to output when you activate the associated peripheral (by some internal logic connected to the peripheral configuration registers). when you look at that, you also see an explanation why it still works when you declare the tx pin as output (as andy kunz observed): you'd just double on what the internal "peripheral oe" does (that's the or gate for /q from the tris latch and the peripheral oe). but i guess you =have= to declare the rx input as input if you want it to work as rx, since the "peripheral oe" only can =activate= the output driver, it can't =deactivate= them (that's again the same or gate). anyway, i declare both of them as inputs (set the associated trisc bits 6 and 7) and let the internal peripheral logic do its work, as they say in the data sheets. ge

>The documentation is / may not clear in defining the state the Tx port >pin that has to be "set". |no, it is quite clear: it says the bits 6 and 7 of the TRISC register have |to be set, which means the ports would be configured for input (ie. the |output driver would be disabled), if they were just plain ports. if you |have a look at the "portc block diagram (peripheral output override)" of a |data sheet, you see the "peripheral oe" output enable, this is the one that |switches the port to output when you activate the associated peripheral (by |some internal logic connected to the peripheral configuration registers). I think the idea is that you're "supposed" to set the Tx pin to an "input" to disconnect the output data latch and let the hardware handle its "really" being an output; the existing designs use the same output drivers for both UART and "normal pin" modes, so there isn't really a problem with having it set to output; it's possible that future PICs might use slew-limitted drivers or something for the UART and setting the port pins to output could cause contention; doubtful though. As for the Rx pin, having the pin set to output would cause whatever data is being output to appear on the pin, overriding the signal (if any) that was trying to drive it. There may be certain circumstances where this could be useful, though [e.g. you could use that pin by itself to implement a one-wire half-duplex serial bus if you bit-bang transmissions; you'd see your own data looped back in that case].