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8.1.2
I/O Control
R1
0 to R12 are medium voltage NMOS open drain I/O ports, R13 and the R2 port are standard
voltage NMOS open drain I/O ports, and the D port and the R0 and R3 port pins are CMOS three
state I/O ports. The different port types have different circuit structures as follows.
(1) Medium Voltage NMOS Open Drain I/O Pin Circuit: R1
0 to R12 are medium voltage
NMOS open drain I/O ports. I/O through these ports is controlled by the port data registers (PDR)
and the data control registers (DCR). When the DCR bit corresponding to a given pin is 1, that pin
functions as an output pin and when the value in the PDR is 0, the NMOS transistor will turn on
and the pin will output a low level voltage. When the PDR is 1, the pin will go to the high
impedance state.
When a given DCR bit is 0, the corresponding pin will function as an input pin.
(2) Standard Voltage NMOS Open Drain I/O Pin Circuit: R1
3 and R20 to R23 are standard
voltage NMOS open drain I/O ports. I/O through these ports is controlled by the PDR and DCR
registers. When the DCR bit corresponding to a given pin is 1, that pin functions as an output pin
and when the value in the PDR is 0, the NMOS transistor will turn on and the pin will output a
low level voltage. When the PDR is 1, the pin will go to the high impedance state.
When a given DCR bit is 0, the corresponding pin will function as an input pin.
(3) Standard Voltage CMOS Three State I/O Pin Circuit: The D, R0 and R3 ports are standard
voltage CMOS three state I/O ports. I/O is controlled by the PDR registers and the data control
registers (DCD, DCR). When a bit in a DCD or DCR register is 1, the corresponding pin will
function as an output pin and output the value in its PDR. Similarly, if a DCD or DCR bit is 0, the
corresponding pin will function as an input pin.