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Port Configuration Registers (PCR)
Each Port has a set of Port Configuration Regis-
ters (PCR) used for configuration. The contents of
the registers can be accessed by the MCU through
normal READ/WRITE bus cycles at the addresses
offsets in hexadecimal from the base of the CSIOP
register.
The pins of a port are individually configurable and
each bit in the register controls its respective pin.
For example, Bit 0 in a register refers to Bit 0 of its
port. The three Port Configuration Registers
(PCR), shown in
Table 22, are used for setting the
Port configurations. The default Power-up state for
Control Register. Any bit reset to 0 in the Control
Register sets the corresponding port pin to MCU I/
O Mode, and a 1 sets it to Address Out Mode. The
default mode is MCU I/O. Only Ports A and B have
an associated Control Register.
Direction Register. The Direction Register, in
conjunction with the output enable (except for Port
D), controls the direction of data flow in the I/O
Ports. Any bit set to 1 in the Direction Register
causes the corresponding pin to be an output, and
any bit set to 0 causes it to be an input. The default
mode for all port pins is input.
the Port Architecture diagrams for Ports A/B and
C, respectively. The direction of data flow for Ports
A, B, and C are controlled not only by the direction
register, but also by the output enable product
term from the PLD AND Array. If the output enable
product term is not active, the Direction Register
has sole control of a given pin’s direction.
An example of a configuration for a Port with the
three least significant bits set to output and the re-
mainder set to input is shown in
Table 25. Since
Port D only contains three pins (shown in
Figure28), the Direction Register for Port D has only the
three least significant bits active.
Drive Select Register. The Drive Select Register
configures the pin driver as Open Drain or CMOS
for some port pins, and controls the slew rate for
the other port pins. An external pull-up resistor
should be used for pins configured as Open Drain.
A pin can be configured as Open Drain if its corre-
sponding bit in the Drive Select Register is set to a
1. The default pin drive is CMOS.
Note that the slew rate is a measurement of the
rise and fall times of an output. A higher slew rate
means a faster output response and may create
more electrical noise. A pin operates in a high slew
rate when the corresponding bit in the Drive Reg-
ister is set to 1. The default rate is slow slew.
Table 26 shows the Drive Register for Ports A, B,
C, and D. It summarizes which pins can be config-
ured as Open Drain outputs and which pins the
slew rate can be set for.
Table 22. Port Configuration Registers (PCR)
Note: 1. See
Table 26 for Drive Register bit definition.
Table 23. Port Pin Direction Control, Output
Enable P.T. Not Defined
Table 24. Port Pin Direction Control, Output
Enable P.T. Defined
Table 25. Port Direction Assignment Example
Register Name
Port
MCU Access
Control
A,B
WRITE/READ
Direction
A,B,C,D
WRITE/READ
Drive Select1
A,B,C,D
WRITE/READ
Direction Register Bit
Port Pin Mode
0
Input
1
Output
Direction
Register Bit
Output Enable
P.T.
Port Pin Mode
0
Input
0
1
Output
1
0
Output
1
Output
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
1