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USART, setting of TRIS register needed (PIC 16F-types) ?

I'm a little bit confused about the TX and RX pins in UART mode. I checked several PIC types: If you read the text carefully, you will read several times: "bit SPEN () and the TRIS register have to be set in order to configure the TX and RX pins as the USART"

Now look at the schematics of the ports, and see that it doesn't matter to set the TRIS register, because the "peripheral OE" will override these settings.

Which of these 2 is true ???

Why is this contradiction in all manuals (also very old) that I've looked in ???

thanks, Stef Mientki

Reply to
Stef Mientki
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Peripheral function does override the TRIS state (unlike some other peripherals). This can be a PITA sometimes as you can't tri-state TXD without also disabling the receiver.

Reply to
Mike Harrison

hi stef,

here is a code fragment from one of my rs-232 devices ...

banksel TRISB movlw b'10100000' ; bit 7 - set for TX ; bit 5 - set for RX movwf TRISB banksel SPBRG movlw d'11' ; 9600 baud (0% error) @ 7.3728 mhz movwf SPBRG banksel TXSTA movlw b'00100000' ; bit 5 - tx enable ; bit 2 - BRGH movwf TXSTA banksel RCSTA movlw b'10010000' ; bit 7 - serial enable ; bit 4 - rx enable movwf RCSTA banksel BAUDCTL movlw b'00000000' ; bit 4 - invert ; bit 3 - BRG16 movwf BAUDCTL

you can see in there that i did set the TRISB bits. did i need to ? don't know. all i can say for sure is that this code does indeed work, it's a working 9600 baud 8n1 serial connection between a laptop and the pic. that's implemented on a 16F690 running at 7.3728 mhz.

hope that helps ...

Stef Mientki wrote:

Reply to
purple_stars

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