Port 3; Block Diagram Of P30 To P37 - NEC mPD780208 Subseries User Manual

4.2.4 Port 3

Port 3 is an 8-bit I/O port with an output latch. The P30 to P37 pins can be set to input mode/output mode in
1-bit units using port mode register 3 (PM3). When the P30 to P37 pins are used as input port pins, on-chip pull-
up resistors can be connected to them in 8-bit units using the pull-up resistor option register (PUO).
In mask ROM versions, use of pull-down resistors can be specified in 1-bit units with the mask option. The
µ PD78P0208 does not contain pull-down resistors.
Port 3 can drive LEDs directly.
Alternate functions include timer I/O, clock output, and buzzer output.
RESET input sets port 3 to input mode.
Figure 4-7 shows a block diagram of port 3.
WR
PUO
RD
WR
PORT
WR
PM
Alternate function
PUO: Pull-up resistor option register
PM: Port mode register
RD: Port 3 read signal
WR: Port 3 write signal
88
CHAPTER 4 PORT FUNCTIONS
Figure 4-7. Block Diagram of P30 to P37
PUO3
Selector
Output latch
(P30 to P37)
PM30 to PM37
User's Manual U11302EJ4V0UM
V
DD
P-ch
P30/TO0 to P32/TO2,
P33/TI1,
P34/TI2,
P35/PCL,
P36/BUZ,
P37
Mask option
Only mask ROM versions.
µ
The PD78P0208
has no pull-down
resistors.