NEC PD78214 - Manual (Page 91)

62
µ
PD78214 Sub-Series
5.2.3 Operation
Port 0 is an output-only port.
Once port 0 is put in the output mode, the output latch becomes operable, enabling data transfer between the
output latch and accumulator according to a transfer instruction. The output latch can be loaded with any data
by a logical operation instruction. Once the output latch is loaded with some data, it retains the data until it is
loaded with other data.
If port 0 is specified to be a real-time output port, no data can be written to the output latch. However, it is possible
to read the contents of the output latch if it is in the real-time output port mode.
Fig. 5-4 Port Specified as an Output Port
5.2.4 Built-In Pull-Up Resistor
Port 0 has no built-in pull-up resistor.
5.2.5 Driving Transistors
Because port 0 has an enhanced driving capacity for the high level side of the output buffer, it can drive a transistor
directly on an active-high signal.
Fig. 5-5 shows an example of connecting a transistor to the port.
Fig. 5-5 Example of Driving a Transistor
P0n
n = 0 to 7
Internal bus
WR PORT
RD
OUT
Output
Iatch
V DD
Load
P0n