MSSP with 16F876A - Electronic Circuits Projects Diagrams Free

ArtemisGoldfish · 19th May 2008, 02:51 PM

I feel completely retarded not being able to figure out what went wrong. Here's the code, it's just meant to send a repeating pulse out of SDO by using the MSSP module in Master mode.

Code:

list p=16f876A
#include <p16f876a.inc>

main:		BSF STATUS,RP0
		MOVLW 0x07
		MOVWF ADCON1
		BCF TRISC,5
		BCF TRISC,3
		BSF TRISC,4
		BSF SSPCON,5
		BCF STATUS,RP0
ser:		BTFSS SSPSTAT,BF
		GOTO ser
		MOVLW 0x66
		MOVWF SSPBUF
		GOTO ser
		END

The first few lines make sure that all the ports on the device are digital (Lest I want to expand the code to somehow use PortA). I use the bit setting to set up the direction of the serial pins to what the datasheet says to use (Clear bit 5 and 3, set 4), and I set the SPI enable bit in SSPCON. (Switch back to Bank 0)

I check the SSPSTAT<BF> bit to check if the serial shift register is done outputting, goes back to wait for it if it's not ready, or puts 0x66 in to send if it is done. As far as the datasheet says, as soon as there is data in the SSPBUF, it's supposed to shift it out, but it just sits there with the pins high. I must've made an obvious mistake that someone can point out, right?

Pommie · 19th May 2008, 03:00 PM

Don't you have to send something before you can get a buffer full condition and once you get BF then you need to read it to prevent a collision.

Mike.

ArtemisGoldfish · 19th May 2008, 03:05 PM

If I'm looking at it and it's 0 because the buffer is empty, it should work fine with the condition.

Pommie · 19th May 2008, 03:07 PM

Quote:

Originally Posted by ArtemisGoldfish

If I'm looking at it and it's 0 because the buffer is empty, it should work fine with the condition.

Won't it wait forever?

Mike.

ArtemisGoldfish · 19th May 2008, 03:11 PM

Hahah, now that you mention it, I maybe should've used BTFSC. I also noticed that I was trying to read from SSPSTAT in the wrong bank. I'll fix these and see what happens.

Pommie · 19th May 2008, 03:21 PM

Quote:

Originally Posted by ArtemisGoldfish

Hahah, now that you mention it, I maybe should've used BTFSC. I also noticed that I was trying to read from SSPSTAT in the wrong bank. I'll fix these and see what happens.

I don't think that will cure the problem. Try writing to SSPBUF, then wait for BF, then read SSPBUF, then loop.

Mike.

ArtemisGoldfish · 19th May 2008, 03:33 PM

Code:

list p=16f876A
#include <p16f876a.inc>

main:		BSF STATUS,RP0   ;Initializing stuff in Bank 1
		MOVLW 0x07
		MOVWF ADCON1
		BCF TRISC,5
		BCF TRISC,3
		BSF TRISC,4
		BSF SSPCON,5     ;Set the SSP Enable bit
		BCF STATUS,RP0  ;Back to Bank 0
ser:		CALL cond
		BTFSC 0x20,0
		GOTO ser
		MOVLW 0x66
		MOVWF SSPBUF
		GOTO ser
cond:		BSF STATUS,RP0
		MOVF SSPSTAT,W
		BCF STATUS,RP0
		MOVWF 0x20
		RETURN
		END

This time I use the cond routine to go into Bank 1, copy the SSPSTAT register to W, go back to Bank 0, and put W into a general purpose register. I BTFSC the BF bit to see if it's not set, if it's all fine, it goes and writes into SSBUF. In the simulator I'm using, it actually gets to writing 0x66 to SSPBUF, but for some reason, the simulator doesn't/can't properly execute the BSF SSPCON,5 instruction. (Using Oshonsoft's PIC Simulator) In the space where it usually says the instruction, when I step through, the BSF SSPCON,5 instruction just appears as "BSF". Could just be a problem with the simulator now, I'll have to test the program on the real hardware when I get my ICD2.

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19th May 2008, 02:51 PM	(permalink)
ArtemisGoldfish	MSSP with 16F876A I feel completely retarded not being able to figure out what went wrong. Here's the code, it's just meant to send a repeating pulse out of SDO by using the MSSP module in Master mode. Code: list p=16f876A #include <p16f876a.inc> main: BSF STATUS,RP0 MOVLW 0x07 MOVWF ADCON1 BCF TRISC,5 BCF TRISC,3 BSF TRISC,4 BSF SSPCON,5 BCF STATUS,RP0 ser: BTFSS SSPSTAT,BF GOTO ser MOVLW 0x66 MOVWF SSPBUF GOTO ser END The first few lines make sure that all the ports on the device are digital (Lest I want to expand the code to somehow use PortA). I use the bit setting to set up the direction of the serial pins to what the datasheet says to use (Clear bit 5 and 3, set 4), and I set the SPI enable bit in SSPCON. (Switch back to Bank 0) I check the SSPSTAT<BF> bit to check if the serial shift register is done outputting, goes back to wait for it if it's not ready, or puts 0x66 in to send if it is done. As far as the datasheet says, as soon as there is data in the SSPBUF, it's supposed to shift it out, but it just sits there with the pins high. I must've made an obvious mistake that someone can point out, right? __________________ <-- Feel free to IM me for random chit-chat and PIC assembly talk Adobe After Effects lets you save your work before it crashes, now THAT'S user-friendly.

19th May 2008, 03:00 PM	(permalink)
Pommie	Don't you have to send something before you can get a buffer full condition and once you get BF then you need to read it to prevent a collision. Mike.

19th May 2008, 03:05 PM	(permalink)
ArtemisGoldfish	If I'm looking at it and it's 0 because the buffer is empty, it should work fine with the condition. __________________ <-- Feel free to IM me for random chit-chat and PIC assembly talk Adobe After Effects lets you save your work before it crashes, now THAT'S user-friendly.

19th May 2008, 03:11 PM	(permalink)
ArtemisGoldfish	Hahah, now that you mention it, I maybe should've used BTFSC. I also noticed that I was trying to read from SSPSTAT in the wrong bank. I'll fix these and see what happens. __________________ <-- Feel free to IM me for random chit-chat and PIC assembly talk Adobe After Effects lets you save your work before it crashes, now THAT'S user-friendly.

19th May 2008, 03:33 PM	(permalink)
ArtemisGoldfish	Code: list p=16f876A #include <p16f876a.inc> main: BSF STATUS,RP0 ;Initializing stuff in Bank 1 MOVLW 0x07 MOVWF ADCON1 BCF TRISC,5 BCF TRISC,3 BSF TRISC,4 BSF SSPCON,5 ;Set the SSP Enable bit BCF STATUS,RP0 ;Back to Bank 0 ser: CALL cond BTFSC 0x20,0 GOTO ser MOVLW 0x66 MOVWF SSPBUF GOTO ser cond: BSF STATUS,RP0 MOVF SSPSTAT,W BCF STATUS,RP0 MOVWF 0x20 RETURN END This time I use the cond routine to go into Bank 1, copy the SSPSTAT register to W, go back to Bank 0, and put W into a general purpose register. I BTFSC the BF bit to see if it's not set, if it's all fine, it goes and writes into SSBUF. In the simulator I'm using, it actually gets to writing 0x66 to SSPBUF, but for some reason, the simulator doesn't/can't properly execute the BSF SSPCON,5 instruction. (Using Oshonsoft's PIC Simulator) In the space where it usually says the instruction, when I step through, the BSF SSPCON,5 instruction just appears as "BSF". Could just be a problem with the simulator now, I'll have to test the program on the real hardware when I get my ICD2. __________________ <-- Feel free to IM me for random chit-chat and PIC assembly talk Adobe After Effects lets you save your work before it crashes, now THAT'S user-friendly.