CHAPTER 4 PORT FUNCTIONS
User’s Manual U17446EJ3V1UD
54
4.2.3 Port
3
Pins P30 to P33 constitute a 4-bit I/O port with an output latch. Each bit of this port can be set to the input or
output mode by using port mode register 3 (PM3). When the P30 to P33 pins are used as an input port, an on-chip
pull-up resistor can be connected in 1-bit units by using pull-up resistor option register 3 (PU3).
The P30 and P31 pins are also used for both timer I/O and external interrupt request input pin functions.
Generation of reset signal sets port 3 to the input mode.
P34 is a 1-bit input-only port. This pin is also used as a RESET pin, and when the power is turned on, this is the
reset function.
For settings of alternate function, refer to
CHAPTER 18 OPTION BYTE
. When using P34 as input port, pull up the
P34 pin by using external resistor.
Figures 4-4 to 4-7 show the block diagrams of port 3.
Figure 4-4. Block Diagram of P30
P30/TI000/INTP0
WR
PU
RD
WR
PORT
WR
PM
PU30
Output latch
(P30)
PM30
V
DD
P-ch
PU3
PM3
Internal bus
Selector
Alternate
function
P3
PU3:
Pull-up resistor option register 3
P3:
Port register 3
PM3:
Port mode register 3
RD:
Read signal
WR
××
: Write signal