Issue with PIC 16F627 RB2 line with UART enabled

[gbsallery]

Hello all,

I'm new to this forum, but just wondering if I could pick your assorted brains on a PIC related issue (no pun intended, honest).

I'm building PWM LED multiplex driver using a PIC 16F627A; thanks to other posts on this forum I've got my driver transistors working correctly for rows and columns, and my software PWM code is working nicely. However, I am unable to get the column attached to pin RB2/TX/CK to function; I suspect that this is because I am using the PIC's UART to talk to a host computer over RS232. Although the port is set as an output in the TRISB register, I have a nagging feeling that enabling the UART forces this to be the serial transmit pin. Is this the case?

Thanks,

Gavin

 

[motion]

From the schematic of the RB2 I/O pin, once the serial port is enabled and TRIS register is set for output, the TX data from the USART prevails over the output latch.

 

[gbsallery]

Ah, thanks. Those diagrams are a little beyond me, I must be rusty...

On a similar note, I'm not getting any ouput from RA4 (RA7,6,3-0 work okay). Could this be something similar? I'm not (intentionally) using the comparator, so I don't think that's it... my initialisation code is shown below, in case that helps.

Gavin

; ****************************
; ** RESET : Boot from here **
; ****************************
RESET	MOVLW	B'00000111' ;Disable comparators
		MOVWF	CMCON
		;
		BSF		STATUS,RP0	;Switch to register bank 1
		MOVLW	B'11010111'
		MOVWF	OPTION_REG
		;
		CLRF	INTCON		;Disable interrupts
		MOVLW	B'00000010'	;RB1 is an input
		MOVWF	TRISB		
		MOVLW	B'00100000'	;All RA ports are outputs, except RA5
		MOVWF	TRISA
;		MOVLW	D'1'		;SPBRG=1 for 115,200 baud (4MHz clock)
		MOVLW	D'12'		;SPBRG=12 for 19,200 baud
		MOVWF	SPBRG
		MOVLW	B'00000100'	;BRGH=High
		MOVWF	TXSTA
		BCF		STATUS,RP0	;Switch back to register bank 0
		MOVLW	B'10010000'	;Enable asynch serial port
		MOVWF	RCSTA
		CLRF	PORTB
		CLRF	PORTA
		CLRF	PACKET_PTR
		CLRF	DIGIT_STAT
		CLRF	PWM_PTR

 

[Nigel Goodwin]

On a similar note, I'm not getting any ouput from RA4 (RA7,6,3-0 work okay).

RA4 is an open-collector output, you need a pull-up resistor for it to go high, it's a really common mistake!.