Post by thread:Polling PortA

I want to use portA to read two switches for one project and four switches for another. How do I make each bit rotate through the carry flag consecutivly. I have been using the following code, but it only reads the first bit. I am using a 16c56 movlw 0x0F tris PORTA movlw 0x00 tris PORTB input bcf STATUS, C rrf PORTA, W btfsc STATUS, C goto code_1 rrf PORTA, W btfsc STATUS, C goto code_2 goto input I was able to write the rest of this program and simulate it with success and I have been stareing at this part for four hours with no luck. Scott

Scott wrote: {Quote hidden}> > I want to use portA to read two switches for one project and four > switches for another. How do I make each bit rotate through the carry > flag consecutivly. I have been using the following code, but it only > reads the first bit. I am using a 16c56 > > movlw 0x0F > tris PORTA > movlw 0x00 > tris PORTB > > input bcf STATUS, C > rrf PORTA, W > btfsc STATUS, C > goto code_1 > rrf PORTA, W > btfsc STATUS, C > goto code_2 > goto input > > I was able to write the rest of this program and simulate it with > success and I have been stareing at this part for four hours with no > luck. > > Scott Try this input movf portA,w movwf Temp rrf Temp btfsc status,C goto code_1 rrf Temp btfsc status,C goto code_2 etc.... goto input You don't need to preclear the carry bit because it will be overwritten on the first rrf instruction anyway. -- Best regards Tony http://www.picnpoke.com Email spam_OUTsalesTakeThisOuTpicnpoke.com

Tony I did not expect to get a response so fast, thanks. However the code that you supplied executed in exactly the same way as my original code. It seems that when I rrf the a register the first bit is sent to the carry. When the instruction comes around a second time it again shifts the first bit into the carry instead of the second bit. Scott Tony Nixon wrote: {Quote hidden}> Scott wrote: > > > > I want to use portA to read two switches for one project and four > > switches for another. How do I make each bit rotate through the carry > > flag consecutivly. I have been using the following code, but it only > > reads the first bit. I am using a 16c56 > > > > movlw 0x0F > > tris PORTA > > movlw 0x00 > > tris PORTB > > > > input bcf STATUS, C > > rrf PORTA, W > > btfsc STATUS, C > > goto code_1 > > rrf PORTA, W > > btfsc STATUS, C > > goto code_2 > > goto input > > > > I was able to write the rest of this program and simulate it with > > success and I have been stareing at this part for four hours with no > > luck. > > > > Scott > > Try this > > input movf portA,w > movwf Temp > rrf Temp > btfsc status,C > goto code_1 > rrf Temp > btfsc status,C > goto code_2 > > etc.... > goto input > > You don't need to preclear the carry bit because it will be overwritten > on the first rrf instruction anyway. > > -- > Best regards > > Tony > > http://www.picnpoke.com > Email .....salesKILLspam@spam@picnpoke.com

Tony Ignore that last reply, the code worked tanks alot. apparently portA can't be rotated. Scott Tony Nixon wrote: {Quote hidden}> Scott wrote: > > > > I want to use portA to read two switches for one project and four > > switches for another. How do I make each bit rotate through the carry > > flag consecutivly. I have been using the following code, but it only > > reads the first bit. I am using a 16c56 > > > > movlw 0x0F > > tris PORTA > > movlw 0x00 > > tris PORTB > > > > input bcf STATUS, C > > rrf PORTA, W > > btfsc STATUS, C > > goto code_1 > > rrf PORTA, W > > btfsc STATUS, C > > goto code_2 > > goto input > > > > I was able to write the rest of this program and simulate it with > > success and I have been stareing at this part for four hours with no > > luck. > > > > Scott > > Try this > > input movf portA,w > movwf Temp > rrf Temp > btfsc status,C > goto code_1 > rrf Temp > btfsc status,C > goto code_2 > > etc.... > goto input > > You don't need to preclear the carry bit because it will be overwritten > on the first rrf instruction anyway. > > -- > Best regards > > Tony > > http://www.picnpoke.com > Email salesKILLspampicnpoke.com

Scott wrote: > > Tony > > I did not expect to get a response so fast, thanks. However the > code that you supplied executed in exactly the same way as my original > code. It seems that when I rrf the a register the first bit is sent to the > carry. When the instruction comes around a second time it again shifts the > first bit into the carry instead of the second bit. > Yes, that would be correct because you read PortA again and reloaded 'Temp' with this data. However, if any switches are set, then the appropriate 'code_x' routine will have executed before returning to the loop. I guess you have appropriate code in these routines to handle debouncing, use switch once and discard, or repeat, and to detect when it releases. It is best to read the port once to get the switch information, rather than to use the 'rrf' instruction on it repeatedly. -- Best regards Tony http://www.picnpoke.com Email .....salesKILLspam.....picnpoke.com

Scott, The problem here is that every time you 'RRF PORTA', the entire port it read, and the first bit is rotated into the C bit. Rather than rotating the port each time, you need to read the port into memory first, then rotate that data. Example: (sorry for the mixed Parallax & Microchip mnemonics) movw porta movf myvar, w rrf myvar btfsc status, c goto code1 rrf myvar btfsc status, c goto code2 . . . Only problem this creates is that any changes in portA during processing are not recognized until next time through this code. Mitch Miller Omaha, NE EraseMEmdmiller2spam_OUTTakeThisOuThome.com {Original Message removed}

part 0 2943 bytes content-type:text/x-vcard; charset=us-ascii; (decoded 7bit) why not try this readkey btfss porta,0 goto key1_press btfss porta,1 goto key2_press retlw 00 key1_press call debounce btfsc porta,0 retlw 00h retlw 01h key2_press call debounce btfsc porta,1 retlw 00h retlw 02h Regards Pailoor "Mitchell D. Miller" wrote: {Quote hidden}> > Scott, > > The problem here is that every time you 'RRF PORTA', the entire port it > read, and the first bit is rotated into the C bit. Rather than rotating the > port each time, you need to read the port into memory first, then rotate > that data. Example: (sorry for the mixed Parallax & Microchip mnemonics) > > movw porta > movf myvar, w > rrf myvar > btfsc status, c > goto code1 > rrf myvar > btfsc status, c > goto code2 > . > . > . > > Only problem this creates is that any changes in portA during processing are > not recognized until next time through this code. > > Mitch Miller > Omaha, NE > mdmiller2spam_OUThome.com > > {Original Message removed}

Sorry, got the two examples mixed up. Tony's example does return the value to the register. (Not used to not showing a destination) Quentin Quentin wrote: > > Here is your problem: > When you rotate the Temp reg, you store the result in W, this is wrong. > You should store it back into the Temp register. If you store it in W > the value in Temp does not change, that's why you are reading the same > bit. > > Quentin

On Tue, 19 Oct 1999, Scott wrote: > Tony > > Ignore that last reply, the code worked tanks alot. apparently > portA can't be rotated. Correct. And - besides - if you rotate something into W, the original will remain unchanged. If you repeat, you get the same result again. (That is why Scott's code does not "exactly the same" as Tony's.) Regards, Imre {Quote hidden}> > Scott > > Tony Nixon wrote: > > > Scott wrote: > > > > > > I want to use portA to read two switches for one project and four > > > switches for another. How do I make each bit rotate through the carry > > > flag consecutivly. I have been using the following code, but it only > > > reads the first bit. I am using a 16c56 > > > > > > movlw 0x0F > > > tris PORTA > > > movlw 0x00 > > > tris PORTB > > > > > > input bcf STATUS, C > > > rrf PORTA, W > > > btfsc STATUS, C > > > goto code_1 > > > rrf PORTA, W > > > btfsc STATUS, C > > > goto code_2 > > > goto input > > > > > > I was able to write the rest of this program and simulate it with > > > success and I have been stareing at this part for four hours with no > > > luck. > > > > > > Scott > > > > Try this > > > > input movf portA,w > > movwf Temp > > rrf Temp > > btfsc status,C > > goto code_1 > > rrf Temp > > btfsc status,C > > goto code_2 > > > > etc.... > > goto input > > > > You don't need to preclear the carry bit because it will be overwritten > > on the first rrf instruction anyway. > > > > -- > > Best regards > > > > Tony > > > > http://www.picnpoke.com > > Email @spam@salesKILLspampicnpoke.com > >

It seems to be working pretty well now, however when I use the rlf instruction the data is rolled into the high nibble of the variable temp and the carry never sees is. How can I make the temp variable four bits wide? Thanks for having mercy on such a newbi. Scott Tony Nixon wrote: {Quote hidden}> Scott wrote: > > > > Tony > > > > I did not expect to get a response so fast, thanks. However the > > code that you supplied executed in exactly the same way as my original > > code. It seems that when I rrf the a register the first bit is sent to the > > carry. When the instruction comes around a second time it again shifts the > > first bit into the carry instead of the second bit. > > > > Yes, that would be correct because you read PortA again and reloaded > 'Temp' with this data. > > However, if any switches are set, then the appropriate 'code_x' routine > will have executed before returning to the loop. I guess you have > appropriate code in these routines to handle debouncing, use switch once > and discard, or repeat, and to detect when it releases. > > It is best to read the port once to get the switch information, rather > than to use the 'rrf' instruction on it repeatedly. > > -- > Best regards > > Tony > > http://www.picnpoke.com > Email KILLspamsalesKILLspampicnpoke.com

> > I want to use portA to read two switches for one project and four > switches for another. How do I make each bit rotate through the carry > flag consecutivly. I have been using the following code, but it only > reads the first bit. I am using a 16c56 > > > movlw 0x0F > tris PORTA > movlw 0x00 > tris PORTB > > input bcf STATUS, C > rrf PORTA, W This is a problem right here. Since you are sending the result to W, only bit 0 of port A will be transferred to the carry bit. {Quote hidden}> btfsc STATUS, C > goto code_1 > rrf PORTA, W > btfsc STATUS, C > goto code_2 > goto input > > I was able to write the rest of this program and simulate it with > success and I have been stareing at this part for four hours with no > luck. Two ways to solve it: 1. Copy portA to a temp register, then rotate that. 2. Skip the rotate completely and simply poll each bit with a bit test. The reason that a lot of uControllers used rotate for this type of operation ius simply because they couldn't test a bit directly. PIC's can so why not use it. 3. You can mask out the bits in port A you're interested in and loop until a switch is actually pressed. Then do a bit test to figure out which switch was pressed. Just a couple of thoughts. I think PIC's code set has other ways of solving the problem. BAJ

Scott wrote: > > It seems to be working pretty well now, however when I use the rlf instruction > the data is rolled into the high nibble of the variable temp and the carry nev er > sees is. How can I make the temp variable four bits wide? Thanks for havin g > mercy on such a newbi. I think someone sneezed on the wafer before they cut it up and wrapped the bits in prickly plastic. It's given your chip an extra instruction :-) The carry is always changed after a 'rrf' or rlf' instruction. It may not appear to get changed, because the new data bit may be the same as the old. if PortA = 00000010, then movf porta,w movwf temp temp = 00000010 carry could be 0 or 1 - it doesn't matter rrf temp temp = 00000001 - [note: bit 7 is the original carry bit value and could be 1] carry = 0 - carry = original value of temp bit 0 carry = 0 -> key #1 not pressed, loop back and rotate again rrf temp temp = 00000000 - bit 7 = the carry bit value carry = 1 - carry = original value of temp bit 0 carry = 1 -> key #2 is pressed, service the key routine Just looking over your message again, you mentioned "rlf" not "rrf". If you changed this by accident that could be causing your problem. Try using 55h or 0xAA in a register and rotate that left or right to see the effect on the register and the carry bit. -- Best regards Tony http://www.picnpoke.com Email RemoveMEsalesTakeThisOuTpicnpoke.com

Tony I solved the problem by using portb for input and porta for output. tha t way I can rrf for the first bit and rlf for the other three. AAAchzoooo! Damn ther e goes the level one environment!!! Scott Tony Nixon wrote: > Scott wrote: > > > > It seems to be working pretty well now, however when I use the rlf instructi on > > the data is rolled into the high nibble of the variable temp and the carry n ever > > sees is. How can I make the temp variable four bits wide? Thanks for hav ing {Quote hidden}> > mercy on such a newbi. > > I think someone sneezed on the wafer before they cut it up and wrapped > the bits in prickly plastic. It's given your chip an extra instruction > :-) > > The carry is always changed after a 'rrf' or rlf' instruction. It may > not appear to get changed, because the new data bit may be the same as > the old. > > if PortA = 00000010, then > > movf porta,w > movwf temp > > temp = 00000010 > carry could be 0 or 1 - it doesn't matter > > rrf temp > > temp = 00000001 - [note: bit 7 is the original carry bit value and could > be 1] > carry = 0 - carry = original value of temp bit 0 > > carry = 0 -> key #1 not pressed, loop back and rotate again > > rrf temp > > temp = 00000000 - bit 7 = the carry bit value > carry = 1 - carry = original value of temp bit 0 > > carry = 1 -> key #2 is pressed, service the key routine > > Just looking over your message again, you mentioned "rlf" not "rrf". If > you changed this by accident that could be causing your problem. > > Try using 55h or 0xAA in a register and rotate that left or right to see > the effect on the register and the carry bit. > > -- > Best regards > > Tony > > http://www.picnpoke.com > Email spamBeGonesalesspamBeGonepicnpoke.com