NEC PD754144 - Manual (Page 98)

CHAPTER 6 PERIPHERAL HARDWARE FUNCTION
98 User’s Manual U10676EJ3V0UM
6.1.4 Operation of digital I/O port
The operations of each port and port pin when a data memory manipulation instruction is executed to manipulate
a digital I/O port differ depending on whether the port is set to the input or output mode (refer to Table 6-3). This
is because, as can be seen from the configuration of the I/O port, the data of each pin is loaded to the internal bus
in the input mode, and the data of the output latch is loaded to the internal bus in the output mode.
(1) Operation in input mode
When a test instruction such as SKT, a bit input instruction such as MOV1, or an instruction that loads port
data to the internal bus in 4-bit units such as IN, MOV, operation, or comparison instructions, is executed,
the data of each pin is manipulated.
When an instruction that transfers the contents of the accumulator in 4-bit units, such as OUT or MOV, is
executed, the data of the accumulator is latched to the output latch. The output buffer remains off.
When the XCH instruction is executed, the data of each pin is input to the accumulator, and the data of the
accumulator is latched to the output latch. The output buffer remains off.
When the INCS instruction is executed, the data (4 bits) of each pin incremented by one (+1) is latched to
the output latch. The output buffer remains off.
When an instruction that rewrites the data memory contents in 1-bit units, such as SET1, CLR1, MOV1, or
SKTCLR, is executed, the contents of the output latch of the specified bit can be rewritten as specified by the
instruction, but the contents of the output latches of the other bits are undefined.
(2) Operation in output mode
When a test instruction, bit input instruction, or an instruction in 4-bit units that loads port data to the internal
bus is executed, the contents of the output latch are manipulated.
When an instruction that transfers the contents of the accumulator in 4-bit units is executed, the data of the
output latch is rewritten and at the same time output from the port pins.
When the XCH instruction is executed, the contents of the output latch are transferred to the accumulator.
The contents of the accumulator are latched to the output latches of the specified port and output from the
port pins.
When the INCS instruction is executed, the contents of the output latches of the specified port are incremented
by 1 and output from the port pins.
When a bit output instruction is executed, the specified bit of the output latch is rewritten and output from the
pin.