Datasheet

 1997-2013 Microchip Technology Inc. Preliminary DS30453E-page 35
PIC16C5X
7.0 I/O PORTS
As with any other register, the I/O Registers can be
written and read under program control. However, read
instructions (e.g., MOVF PORTB,W) always read the I/O
pins independent of the pin’s input/output modes. On
RESET, all I/O ports are defined as input (inputs are at
hi-impedance) since the I/O control registers (TRISA,
TRISB, TRISC) are all set.
7.1 PORTA
PORTA is a 4-bit I/O Register. Only the low order 4 bits
are used (RA<3:0>). Bits 7-4 are unimplemented and
read as '0's.
7.2 PORTB
PORTB is an 8-bit I/O Register (PORTB<7:0>).
7.3 PORTC
PORTC is an 8-bit I/O Register for PIC16C55,
PIC16C57 and PIC16CR57.
PORTC is a General Purpose Register for PIC16C54,
PIC16CR54, PIC16C56, PIC16CR56, PIC16C58 and
PIC16CR58.
7.4 TRIS Registers
The Output Driver Control Registers are loaded with
the contents of the W Register by executing the
TRIS f instruction. A '1' from a TRIS Register bit puts
the corresponding output driver in a hi-impedance
(input) mode. A '0' puts the contents of the output data
latch on the selected pins, enabling the output buffer.
The TRIS Registers are “write-only” and are set (output
drivers disabled) upon RESET.
7.5 I/O Interfacing
The equivalent circuit for an I/O port pin is shown in
Figure 7-1. All ports may be used for both input and
output operation. For input operations these ports are
non-latching. Any input must be present until read by
an input instruction (e.g., MOVF PORTB, W). The out-
puts are latched and remain unchanged until the output
latch is rewritten. To use a port pin as output, the corre-
sponding direction control bit (in TRISA, TRISB,
TRISC) must be cleared (= 0). For use as an input, the
corresponding TRIS bit must be set. Any I/O pin can be
programmed individually as input or output.
FIGURE 7-1: EQUIVALENT CIRCUIT
FOR A SINGLE I/O PIN
TABLE 7-1: SUMMARY OF PORT REGISTERS
Note: A read of the ports reads the pins, not the
output data latches. That is, if an output
driver on a pin is enabled and driven high,
but the external system is holding it low, a
read of the port will indicate that the pin is
low.
Note 1: I/O pins have protection diodes to VDD and VSS.
Data
Bus
QD
Q
CK
QD
Q
CK
P
N
WR
Port
TRIS ‘f’
Data
TRIS
RD Port
V
SS
VDD
I/O
pin
(1)
W
Reg
Latch
Latch
RESET
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-On
Reset
Value on
MCLR and
WDT Reset
N/A TRIS I/O Control Registers (TRISA, TRISB, TRISC) 1111 1111 1111 1111
05h PORTA
— — — — RA3 RA2 RA1 RA0 ---- xxxx ---- uuuu
06h PORTB RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 xxxx xxxx uuuu uuuu
07h PORTC RC7 RC6 RC5 RC4 RC3 RC2 RC1 RC0 xxxx xxxx uuuu uuuu
Legend: x = unknown, u = unchanged, — = unimplemented, read as '0', Shaded cells = unimplemented, read as ‘0’