16F84 Physical Input and Output

The 16F84 has 13 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 16F84, 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 16F84 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

LABEL	PIN		PIN DIAGRAM
RA0	17
RA1	18
RA2	1
RA3	2
RA4	3
RB0	6
RB1	7
RB2	8
RB3	9
RB4	10
RB5	11
RB6	12
RB7	13

sample projects (ciruits, sample code and chip programming)

XCSB compiler

Writing to a specific pin

To write to pin 1 of a 16F84 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	N/A	N/A	N/A	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	N/A	N/A	N/A	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	N/A	N/A	N/A	3	2	1	18	17

This can be done in XCSB as:

// 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 | 0x04

The 0x04 value is a hex mask (the equivalent of binary 00000100 see binary to hex).

A 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 operator

To 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 numbers

To set pins 1 and 17 to 1 use

TRISA = TRISA & ~((1 << 2) | (1 << 0))
PORTA = PORTA | ((1 << 2) | (1 << 0))

More about bit manipulation and binary

Reading from a specific pin

To read from pin 1 of a 16F84 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	N/A	N/A	N/A	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	N/A	N/A	N/A	3	2	1	18	17

Then read from PORTA and mask out bit 2

This can be done in XCSB as:

// 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 0x04

The 0x04 value is a hex mask (the equivalent of binary 00000100 see binary to hex).

A 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 operator

The 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 0x04

More about bit manipulation and binary