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CHAPTER 4 I/O PORTS
4.3.2
Operation of Port 1
This section describes the operations of the port 1.
I Operation of port 1
G
Operation as an output port
• When the output latch value is "0", the output transistor turns "ON" and an "L" level is output from the
pin. When the output latch value is "1", the transistor turns "OFF" and high impedance (Hi-Z) is output
from the pin.
• Writing data to the PDR1 register stores the data in the output latch and it will be output to the pin.
• Reading the PDR1 register returns the output latch value.
G
Operation as an input port
• Writing "0" to the PDR1 register set the port as an input port, the output transistor is "OFF" and the pin
goes to the high-impedance state.
• Reading the PDR1 register returns the pin value.
G
Operation as an LCD segment driver output
• When the LCD output mask option is selected, set the PDR1 register bits corresponding to the LCD
segment driver output pins to "1" to turn the output transistor "OFF".
• You cannot read the LCD output data by reading PDR1.
G
Operation at reset
• Resetting the CPU initializes the PDR1 register values to "1". This turns "OFF" the output transistor for
all pins and all pins are in high impedance (Hi-Z) state.
80
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