The 16F88 has 16 I/O pins
These pins are accessed via port A and B
To identify which bit within which port is responsible for driving a particular PIC pin, look at the pin diagram below (this diagram is only good for the 16F88, refer to other pin diagrams for other PICs). Locate the pin you are interested in and read off the label.
The label will be of the form Rxj
where x will be A for PORTA, B for PORTB etc., and j will be the bit number within the port (in the range 0 to 7)
On the 16F88 port A bit 0 connects to the pin labelled RA0 which is pin 17, port A bit 3 connects to the pin labelled RA3 which is pin 2
NOTE: most of the I/O pins on the 16F88 have multiple functions and multiple labels to indicate these functions. When using a pin it must be configured to perform the required function. This is done internally by the program when it starts running. The program writes to special function registers which are responsible for configuring the pins.
sample projects (ciruits, sample code and chip programming)
LABEL PIN PIN DIAGRAM RA0 17 RA1 18 RA2 1 RA3 2 RA4 3 RA5 4 RA6 15 RA7 16 RB0 6 RB1 7 RB2 8 RB3 9 RB4 10 RB5 11 RB6 12 RB7 13
To write to pin 1 of a 16F88 lookup the label on pin 1 in the pin diagram. The label is RA2. This translates to PORTA bit 2.
BIT NUMBER 7 6 5 4 3 2 1 0 PORTA x x x x x x x x TRISA x x x x x x x x PIN LABEL RA7 RA6 RA5 RA4 RA3 RA2 RA1 RA0 PIN NUMBER 16 15 4 3 2 1 18 17 Clear the corresponding bit in the PORTA data direction register (called TRISA) to 0, that is clear TRISA bit 2 to 0. This configures pin 1 as an output.
BIT NUMBER 7 6 5 4 3 2 1 0 PORTA x x x x x x x x TRISA x x x x x 0 x x PIN LABEL RA7 RA6 RA5 RA4 RA3 RA2 RA1 RA0 PIN NUMBER 16 15 4 3 2 1 18 17 Then write the required value (0 or 1) to PORTA bit 2
BIT NUMBER 7 6 5 4 3 2 1 0 PORTA x x x x x 0 or 1 x x TRISA x x x x x 0 x x PIN LABEL RA7 RA6 RA5 RA4 RA3 RA2 RA1 RA0 PIN NUMBER 16 15 4 3 2 1 18 17 This can be done in XCSB as:
The 0x04 value is a hex mask (the equivalent of binary 00000100 see binary to hex).// configure pin 1 as output by writing 0 to TRISA bit 2 TRISA = TRISA & ~0x04 // set pin 1 low (to 0) by writing 0 to PORTA bit 2 PORTA = PORTA & ~0x04 // set pin 1 high (to 1) by writing 1 to PORTA bit 2 PORTA = PORTA | 0x04A simpler way to access a bit within a byte is to use a constant expression of the form
(1 << n)where n is the bit number and << is the left shift operatorTo access multiple bits within a byte, combine them with the bit wise OR operator
e.g.(1 << n) | (1 << m) | (1 << j)where n, m and j are the bit numbersTo set pins 1 and 17 to 1 use
More about bit manipulation and binaryTRISA = TRISA & ~((1 << 2) | (1 << 0)) PORTA = PORTA | ((1 << 2) | (1 << 0))
To read from pin 1 of a 16F88 lookup the label on pin 1 in the pin diagram. The label is RA2. This translates to PORTA bit 2.
BIT NUMBER 7 6 5 4 3 2 1 0 PORTA x x x x x x x x TRISA x x x x x x x x PIN LABEL RA7 RA6 RA5 RA4 RA3 RA2 RA1 RA0 PIN NUMBER 16 15 4 3 2 1 18 17 Set the corresponding bit in the PORTA data direction register (called TRISA) to 1, that is set TRISA bit 2 to 1. This configures pin 1 as an input.
BIT NUMBER 7 6 5 4 3 2 1 0 PORTA x x x x x x x x TRISA x x x x x 1 x x PIN LABEL RA7 RA6 RA5 RA4 RA3 RA2 RA1 RA0 PIN NUMBER 16 15 4 3 2 1 18 17 Then read from PORTA and mask out bit 2
This can be done in XCSB as:
The 0x04 value is a hex mask (the equivalent of binary 00000100 see binary to hex).// configure pin 1 as input by writing 1 to TRISA bit 2 TRISA = TRISA | 0x04 // read 0 or 1 into the variable called result result = (PORTA & 0x04) != 0 // NOTE: the expression (PORTA & 0x04) return 0x00 or 0x04 // the expression X != 0 return 0 if X is 0x00 or 1 if X is 0x04A simpler way to access a bit within a byte is to use a constant expression of the form
(1 << n)where n is the bit number and << is the left shift operatorThe above example could then be re-written as:
// configure pin 1 as input by writing 1 to TRISA bit 2 TRISA = TRISA | (1 << 2) // read 0 or 1 into the variable called result result = (PORTA & (1 << 2)) != 0 // NOTE: the expression (PORTA & (1 << 2)) return 0x00 or 0x04 // the expression X != 0 return 0 if X is 0x00 or 1 if X is 0x04More about bit manipulation and binary