RFPIC12C509AG Microchip Technology Inc., RFPIC12C509AG Datasheet - Page 25

• Manufacturer Part Number: RFPIC12C509AG
• Description: 18/20-pin 8-bit Cmos Microcontroller With Uhf Ask/fsk Transmitter
• Manufacturer: Microchip Technology Inc.

5.0
As with any other register, the I/O register can be writ-
ten and read under program control. However, read
instructions (e.g., MOVF GPIO,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 are all set.
5.1
GPIO is an 8-bit I/O register. Only the low order 6 bits
are used (GP5:GP0). Bits 7 and 6 are unimplemented
and read as '0's. Please note that GP3 is an input only
pin. The configuration word can set several I/O’s to
alternate functions. When acting as alternate functions
the pins will read as ‘0’ during port read. Pins GP0,
GP1, and GP3 can be configured with weak pull-ups
and also with wake-up on change. The wake-up on
change and weak pull-up functions are not pin select-
able. If pin 4 is configured as MCLR, weak pull-up is
always on and wake-up on change for this pin is not
enabled.
5.2
The output driver control register is loaded with the
contents of the W register by executing the TRIS f
instruction. A '1' from a TRIS register bit puts the corre-
sponding output driver in a hi-impedance mode. A '0'
puts the contents of the output data latch on the
selected pins, enabling the output buffer. The excep-
tions are GP3 which is input only and GP2 which may
be controlled by the option register, see Figure 4-4.
The TRIS registers are “write-only” and are set (output
drivers disabled) upon RESET.
©
Note:
2001 Microchip Technology Inc.
I/O PORT
GPIO
TRIS Register
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.
Preliminary
rfPIC12C509AG/509AF
5.3
The equivalent circuit for an I/O port pin is shown in
Figure 5-1. All port pins, except GP3 which is input
only, may be used for both input and output operations.
For input operations these ports are non-latching. Any
input must be present until read by an input instruction
(e.g., MOVF GPIO,W). The outputs are latched and
remain unchanged until the output latch is rewritten. To
use a port pin as output, the corresponding direction
control bit in TRIS must be cleared (= 0). For use as an
input, the corresponding TRIS bit must be set. Any I/O
pin (except GP3) can be programmed individually as
input or output.
FIGURE 5-1:
Data
Bus
WR
Port
W
Reg
TRIS ‘f’
Note 1: I/O pins have protection diodes to V
I/O Interfacing
2: See Table 3-1 for buffer type.
D
D
and V
CK
CK
Reset
Data
Latch
TRIS
Latch
EQUIVALENT CIRCUIT
FOR A SINGLE I/O PIN
SS
Q
Q
Q
Q
.
RD Port
(2)
DS70031A-page 23
V
V
P
N
SS
DD
I/O
pin
DD
(1)