M30245_06 Datasheet, PDF (293/367 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/20 SERIES

M30245 Group
2. Programmable I/O Ports
2.17 Programmable I/O Ports Usage
2.17.1 Overview of the programmable I/O ports usage
Eighty-one programmable I/O ports and one input-only port are available. I/O pins also serve as I/O pins
for built-in peripheral functions.
Each port has a direction register that defines the I/O direction and also has a port register for I/O data. In
addition, each port has a pull-up control register that defines pull-up in terms of 4 bits. The input-only port
has neither direction register nor pull-up control bit.
The following is an overview of the programmable I/O ports usage:
(1) Writing to a port register
With the direction register set to output, the level of the written values from each relevant pin is output
by writing to a port register. The output level conforms to CMOS output. Port P70 and P71 are N
channel open drain. Writing to the port register, with the direction register set to input, inputs a value
to the port register, but nothing is output to the relevant pins. The output level remains floating.
In memory expansion and microprocessor mode, the contents of corresponding port and direction
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_______ _____ ________ ______ ________ _______
_______ __________
registers of pins A0 to A19, D0 to D15, CS0 to CS3, RD, WRL/WR, WRH/BHE, ALE, RDY, HOLD,
_________
HLDA and BCLK cannot be modified.
(2) Reading a port register
With the direction register set to output, reading a port register takes out the content of the port regis-
ter, not the content of the pin. With the direction register set to input, reading the port register takes out
the content of the pin.
(3) Input-only port
_______
P85 is used as the input-only port, it also serves as NMI. P85 has no direction register. Pull-up cannot
_______
_______
be set to this port. As NMI cannot be disabled, an NMI interrupt occurs if a falling edge is input to P85.
Use P85 for reading the level input at this time only.
(4) Setting pull-up
The pull-up control bit allows setting of the pull-up, in terms of 4 bits, either in use or not in use. For the
four bits chosen, pull-up is effective only in the ports whose direction register is set to input. Pull-up is
not effective in ports whose direction register is set to output.
Do not set pull-up of corresponding pin when XCIN/XCOUT is set or a port is used as A/D input.
Pull-up can be set for P0 to P3, P40 to P43, P50 to P53 in only single-chip mode. Pull-up cannot be set
for P0 to P3, P40 to P43, P50 to P53 in memory expansion and microprocessor modes. The contents
of register can be changed, but the pull-up resistance is not connected.
(5) Setting drive capacity
A normal drive and N-channel high drive for the N-channel transistor drive capacity of port P7 can be
selected. Port P7 can be configured to drive an LED by increasing the drive strength of the corre-
sponding N-channel transistor bits.
Rev.2.00 Oct 16, 2006 page 284 of 354
REJ09B0340-0200