Indexing Port Pins

[Bruce]

Melanie posted an excellent article on indexing bits, bytes, words, etc. here
http://www.picbasic.co.uk/forum/showthread.php?t=544

Someone asked how to index port pins in a similar way, so here's one way.

Port file register addresses are sequential. For instance on the 16F876A file
register address for porta is at location 05h, portb is at 06h, and portc is at
07h. All you need is a pointer to the base of the bit index.

Example; SYMBOL PORT_PIN = PORTA ' <- start of bit index or pointer

Now using something like this, you can index all port bits.

X VAR BYTE ' For loop & bit index pointer  
ADCON1 = 7 ' All digital
PORTA = 0   ' Clear all port pins
PORTB = 0
PORTC = 0

TRISA = 0   ' Make them all outputs
TRISB = 0
TRISC = 0

FOR X = 0 TO 23
  PORT_PIN.0[X] = 1  ' Set all porta, portb, and portc pins high
NEXT X

There aren't 8 pins on porta that can go high, but it's still an 8-bit file register
so we have to treat it as 8-bit and index from 0 to 23 for 24-bits total.

You can do this on any PIC to index all port pins individually just using porta
as the starting index pointer.

PBP doesn't perfom bounds checking, so you can get away with indexing
out of bounds.

Note that also means you could write to a register you may not intend to if
you're not careful.

You could drop porta, and just use portb as the starting address also.

SYMBOL PORT_PIN = PORTB

X VAR BYTE ' For loop & bit index pointer  

PORTB = 0
PORTC = 0

' Make them all outputs
TRISB = 0
TRISC = 0

FOR X = 0 TO 15 ' 16-bits total
  PORT_PIN.0[X] = 1  ' Set all portb, and portc pins high
NEXT X

[sayzer]

In addition to Bruce's nice examples, and in connection with Melanie's explanations, mixed port pins can be driven in a sequence with the code below. The code is for demonstration purposes and quite easy to figure out.

TRISA  = %00000000 
TRISB  = %00000000 
TRISC  = %00000000 
TRISD  = %00000000 
TRISE  = %00000000
ADCON1 = %00000000 
PORTA  = 0
PORTB  = 0
PORTC  = 0
PORTD  = 0
PORTE  = 0
 
MYPORT VAR BYTE
LOOP   var BYTE

'======Say you have to drive 
'these pins in a sequence. They are all mixed.

RelayA  VAR PORTA.1
RelayB  var PORTA.3
RelayC  var PORTB.5
RelayD  var PORTC.0
RelayE  var PORTD.2
RelayF  var PORTD.4
RelayG  var PORTE.0

MYPORT=0


Start:

    for loop=1 to 7

      myport.0[loop]=1  'High
      gosub driveport  
      
      pause 1000

      myport.0[loop]=0  'Low
      gosub driveport       

    next loop
    
    
goto start



DrivePort:
    RELAYA = myport.1
    RELAYB = MYPORT.2
    RELAYC = MYPORT.3
    RELAYD = MYPORT.4
    RELAYE = MYPORT.5
    RELAYF = MYPORT.6
    RELAYG = MYPORT.7
    return
    
    
    
END

Hope it can be some help to some members.

Regards.

[isaac]

Hi Bruce / sayzer

Just being reading your interesting posts about port indexing
and wanted to know if it was posible to map a variable to different ports
example say like using a word variable to control the 16bits below
How to i go about this? Is it possible ?
RB7 = //MSB
RB6
RB5
RB4
RB3
RB2
RB1
RB0
RA0
RA1
RA2
RA3
RD0
RD1
RD2
RD3 //LSB

Hope you can help

Regards
Isaac

[Bruce]

Hi Isaac,

See this thread for some ideas: http://www.picbasic.co.uk/forum/showthread.php?t=4074

[sayzer]

Hi Bruce / sayzer....
...using a word variable to control the 16bits below
How to i go about this? Is it possible ?...

I do not think you can drive the ports or port pins directly by using alias on them via a the bits of a WORD or BYTE variable.


For example,

MYPORT VAR WORD

PORTA.1 VAR MYPORT.0 is an incorrect arrangement.

MYPORT.0 VAR PORTA.1 is also incorrect.

PORTB VAR MYPORT.HighByte incorrect.

PORTA VAR MYPORT incorrect


But,
PORTB = MYPORT

or

PORTB = MYPORT.HighByte or PORTB = MYPORT.LowByte can be ok!



But anyway, in addition to the link that Bruce posted, here I posted an example with the port pins you listed.

See if it is what you needed.

'Assuming you have the ports set up.

Loop    VAR BYTE
MYPORT  VAR WORD
MYPORT = 0
GOSUB DriveMeCrazy  'Pull all pins low.


Start:
        
        FOR LOOP = 0 TO 15

            MYPORT.0[LOOP] = 1          'HIGH
            GOSUB DriveMeCrazy

            PAUSE 1000                  'Give it a pause as an example.
            
            MYPORT.0[LOOP] = 0          'LOW
            GOSUB DriveMeCrazy
            
        NEXT LOOP
        
        
        GOTO START


    
DriveMeCrazy:

    PORTB.7 = MYPORT.15
    PORTB.6 = MYPORT.14
    PORTB.5 = MYPORT.13
    PORTB.4 = MYPORT.12
    PORTB.3 = MYPORT.11
    PORTB.2 = MYPORT.10
    PORTB.1 = MYPORT.9
    PORTB.0 = MYPORT.8  'From here to above, "PORTB = MYPORT.HighByte" may also be ok.
    PORTA.0 = MYPORT.7  
    PORTA.1 = MYPORT.6
    PORTA.2 = MYPORT.5
    PORTA.3 = MYPORT.4
    PORTD.0 = MYPORT.3
    PORTD.1 = MYPORT.2
    PORTD.2 = MYPORT.1
    PORTD.3 = MYPORT.0
    
    RETURN

[isaac]

Thanks Bruce /sayzer

Your examples did help me get it sorted
you both have being great

Isaac

[Demon]

Update: Cleaned up logic so LEDs always get same current no matter how many are in use.

When you need to blink a lot of LEDs:

Here's the results of a current test using 32 LEDs on a 18F44K22 using internal oscillator at 64MHz.

portLedA    var     PORTA       ' Define Ports
portLedB    var     PORTB
portLedC    var     PORTC
portLedD    var     PORTD
portLedE    var     PORTE

byteLoop    VAR     byte        ' Define variables
byteDelay   VAR     byte

byteActiveA var     byte        ' Define active pins
byteActiveB var     byte
byteActiveC var     byte
byteActiveD var     byte
byteActiveE var     byte

byteRXA     var     byte        ' Define RX data
byteRXB     var     byte
byteRXC     var     byte
byteRXD     var     byte
byteRXE     var     byte

    portLedA = %00000000        ' Initialize Leds off
    portLedB = %00000000
    portLedC = %00000000
    portLedD = %00000000
    portLedE = %00000000

 byteActiveA = %11111110        ' Determine Active pins     Pin A.0 not used
 byteActiveB = %11111111
 byteActiveC = %00111111                                  ' RX / TX in use
 byteActiveD = %11111111
 byteActiveE = %00000111                                  ' MCLR input only

     byteRXA = %11111110        ' RX data from Master PIC
     byteRXB = %11111111                                    
     byteRXC = %00111111
     byteRXD = %11111111
     byteRXE = %00000111

byteDelay    = 35               ' Tweak this value to control current and frequency

' 1 LED active        668 Hz     2.7 mA LED    14.2 mA circuit
' 32 LEDs active      668 Hz     2.7 mA LED    99.0 mA circuit

' Using 2N2222 NPN transistor, 4K7 base with 680K pull-down,
'       LED direct to collector from 5VDC.

mainloop:

    For byteLoop = 0 to 7                       ' Go through 8 bits
        if byteActiveA.0[byteLoop] = 1 then     ' Check if pin is used
            portLedA.0[byteLoop] = byterxA.0[byteLoop]
            PAUSEUS byteDelay
            portLedA = %00000000                ' Faster than setting bit to 0
        endif
        if byteActiveB.0[byteLoop] = 1 then
            portLedB.0[byteLoop] = byterxB.0[byteLoop]
            PAUSEUS byteDelay
            portLedB = %00000000
        endif
        if byteActiveC.0[byteLoop] = 1 then
            portLedC.0[byteLoop] = byterxC.0[byteLoop]
            PAUSEUS byteDelay
            portLedC = %00000000
        endif
        if byteActiveD.0[byteLoop] = 1 then
            portLedD.0[byteLoop] = byterxD.0[byteLoop]
            PAUSEUS byteDelay
            portLedD = %00000000
        endif
        if byteActiveE.0[byteLoop] = 1 then
            portLedE.0[byteLoop] = byterxE.0[byteLoop]
            PAUSEUS byteDelay
            portLedE = %00000000
        endif
    Next byteLoop

    Goto mainloop           ' Go back to loop and blink LEDs forever

Use byteActiveA-E variables to determine which bits you want toggled.

Use byteRXA-E variables to receive bits from a Master PIC.

Use byteDelay variable to tweak current and LED brightness.


For my testing, MCLR (can only be input), RX/TX (needed) and A0 (unused) were disabled.

Robert