Www.datasheet4U.com 4.2.2 Port 3 - NEC 78K0S/KA1+ Preliminary User's Manual

www.DataSheet4U.com
4.2.2 Port 3
Pins P30 and P31 constitute a 2-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 P31 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). This port is also used
as external interrupt request input pins.
The P34 pin is a 1-bit input-only port and functions alternately as the RESET pin.
Reset input sets port 3 to the input mode.
Figures 4-3 and 4-4 show the block diagrams of port 3.
Caution Because the P34 pin functions alternately as the RESET pin, if it is used as an input port pin, the
function to input an external reset signal to the RESET pin cannot be used. The function of the
port is selected by the option byte. For details, refer to CHAPTER 17 OPTION BYTE.
www.DataSheet4U.com
If a low level is input to the RESET pin before the option byte is referenced again after reset is
released by the POC circuit, the 78K0S/KA1+ is reset and is held in the reset state until a high
level is input to the RESET pin.
WR
PU
RD
WR
PORT
WR
PM
PU3:
PM3:
RD:
WR××: Write signal
48
CHAPTER 4 PORT FUNCTIONS
Figure 4-3. Block Diagram of P30 and P31
PU3
PU30, PU31
Alternate
function
Output latch
(P30, P31)
PM3
PM30, PM31
Alternate
function
Pull-up resistor option register 3
Port mode register 3
Read signal
Preliminary User's Manual U16898EJ1V0UD
V
DD
P-ch
P30/TI000/INTP0,
P31/TI010/TO00/INTP2