I/O Question, best way to output a byte on two ports? - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 28th March 2007, 07:41 PM

I have available some I/O on two output ports (PIC)

RA 765x321x
RB xx543xxx

I want one byte of I/O (8 bits) it may be asynchronous.

Any suggestions, ideas?

Sceadwian · 29th March 2007, 12:44 AM

RA looks like it's the most of a full byte,
you could read in the RA byte, use a bitmask to prevent the two x bits from being overwritten and write out your data byte, which will give you all but bits 4 and 0, which you should be able to further mask out from your data byte to the leftover bits on RB. You'd still have 3 extra bits on RB so you could use one of those as a strobe 'data ready' bit if you need it to be synchronous.

That's a bit of codeing though, you could also just bit bang a synchronous serial shift register. Many people do that to increase the number of I/O pins on non speed sensative designs.

Pommie · 29th March 2007, 02:47 AM

Not very elegant but does the job.

Code:

	movfw	Byte
	andlw	b'11101110'
	movwf	PORTB
	btfss	Byte,0
	bcf	PORTA,3
	btfsc	Byte,0
	bsf	PORTA,3
	btfss	Byte,3
	bcf	PORTA,4
	btfsc	Byte,3
	bsf	PORTA,4

Mike

gramo · 29th March 2007, 03:07 AM

If your using mikroBasic, you could do something like this

Code:

Program Port_Mask

Dim PORTX as Byte

sub procedure Write_Byte(Dim PORTX as Byte)

    TRISA.1 = 0                   ' Change to outputs
    TRISA.2 = 0
    TRISA.3 = 0
    TRISA.5 = 0
    TRISA.6 = 0
    TRISA.7 = 0
    TRISB.3 = 0
    TRISB.4 = 0

    PORTA.1 = PORTX.0        ' Build PORTX's data on the pins
    PORTA.2 = PORTX.1
    PORTA.3 = PORTX.2
    PORTA.5 = PORTX.3
    PORTA.6 = PORTX.4
    PORTA.7 = PORTX.5
    PORTB.3 = PORTX.6
    PORTB.4 = PORTX.7

end sub

sub procedure Read_Byte(Dim PORTX as Byte)

    TRISA.1 = 1                  ' Change to inputs
    TRISA.2 = 1
    TRISA.3 = 1
    TRISA.5 = 1
    TRISA.6 = 1
    TRISA.7 = 1
    TRISB.3 = 1
    TRISB.4 = 1

    PORTX.0 = PORTA.1       ' Build PORTX's data
    PORTX.1 = PORTA.2
    PORTX.2 = PORTA.3
    PORTX.3 = PORTA.5
    PORTX.4 = PORTA.6
    PORTX.5 = PORTA.7
    PORTX.6 = PORTB.3
    PORTX.7 = PORTB.4

end sub

Main:

      PORTX = 123             ' Put the value "123" into PORTX
      Write_Byte(PORTX)     ' Update all of the pins for PORTX

      Read_Byte(PORTX)     ' Read the contents of PORTX

      Write_Byte(234)        ' Write the value "234" to PORTX

      Goto Main
End.

donniedj · 29th March 2007, 07:38 AM

Quote:

Originally Posted by Pommie

Not very elegant but does the job.

Code:

	movfw	Byte
	andlw	b'11101110'
	movwf	PORTB
	btfss	Byte,0
	bcf	PORTA,3
	btfsc	Byte,0
	bsf	PORTA,3
	btfss	Byte,3
	bcf	PORTA,4
	btfsc	Byte,3
	bsf	PORTA,4

Mike

That is exactly my method of creating a virtual port for 4-bit LCD interfacing. Write to Virtual port and call VP_Update to automatically map individual bits of a byte or bytes to corresponding i/o channels. Either full port masking with mathmatical operators or simple BTFSS, it still elegant in my book. Its elegant because its Virtual

geko · 29th March 2007, 10:12 PM

Code:

 
; W reg contains byte to output
   movwf    portA 
   andlw     0x11
   addlw     0x07
   movwf    portB    ; bit 4 -> i/o 4, bit 0 -> i/o 3

Mike, K8LH · 30th March 2007, 01:01 AM

Quote:

Originally Posted by blueroomelectronics

I have available some I/O on two output ports (PIC)

RA 765x321x
RB xx543xxx

I want one byte of I/O (8 bits) it may be asynchronous.

Any suggestions, ideas?

I'm not sure I understand the question. Could you rephrase?

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28th March 2007, 07:41 PM	(permalink)
blueroomelectronics	I/O Question, best way to output a byte on two ports? I have available some I/O on two output ports (PIC) RA 765x321x RB xx543xxx I want one byte of I/O (8 bits) it may be asynchronous. Any suggestions, ideas? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com Last edited by blueroomelectronics; 29th March 2007 at 12:33 AM.

29th March 2007, 12:44 AM	(permalink)
Sceadwian	RA looks like it's the most of a full byte, you could read in the RA byte, use a bitmask to prevent the two x bits from being overwritten and write out your data byte, which will give you all but bits 4 and 0, which you should be able to further mask out from your data byte to the leftover bits on RB. You'd still have 3 extra bits on RB so you could use one of those as a strobe 'data ready' bit if you need it to be synchronous. That's a bit of codeing though, you could also just bit bang a synchronous serial shift register. Many people do that to increase the number of I/O pins on non speed sensative designs. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 29th March 2007 at 12:46 AM.

29th March 2007, 02:47 AM	(permalink)
Pommie	Not very elegant but does the job. Code: movfw Byte andlw b'11101110' movwf PORTB btfss Byte,0 bcf PORTA,3 btfsc Byte,0 bsf PORTA,3 btfss Byte,3 bcf PORTA,4 btfsc Byte,3 bsf PORTA,4 Mike

29th March 2007, 10:12 PM	(permalink)
geko	Code: ; W reg contains byte to output movwf portA andlw 0x11 addlw 0x07 movwf portB ; bit 4 -> i/o 4, bit 0 -> i/o 3 __________________ Pete picprojects.org.uk Last edited by geko; 29th March 2007 at 10:17 PM.