CR16MCS5 datasheet(13/156 Pages) NSC

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6.0

Input/Output Ports

Each device has up to 56 software-configurable I/O pins, or-

ganized into seven ports of up to eight pins per port. The

ports are named Port B, Port C, Port F, Port G, Port H, Port

I, and Port L.

Each pin can be configured to operate as a general-purpose

input or general-purpose output. In addition, many I/O pins

can be configured to operate as a designated input or output

for an on-chip peripheral module such as the USART or the

Multi-Input Wakeup. This is called the pin's “alternate func-

tion.” The alternate functions of all I/O pins are shown in the

pinout diagrams in Table1.

The I/O pin characteristics are fully programmable. Each pin

can be configured to operate as a TRI-STATE output, push-

pull output, weak pull-up input, or high-impedance input. Dif-

ferent pins within the same port can be individually config-

ured to operate in different modes.

Figure1 is a diagram showing the functional features of an I/

O port pin. The register bits, multiplexers, and buffers allow

the port pin to be configured into the various operating

modes.The output buffer is a TRI-STATE buffer with weak

pull-up capability. The weak pull-up, if used, prevents the port

pin from going to an undefined state when it operates as an

input.

The input buffer is disabled when it is not needed to prevent

leakage current caused by an input signal’s level between

Vcc-0.2 and Vss+0.2 [Volts]. When enabled, it buffers the in-

put signal and sends the pin's logic level to the appropriate

on-chip module where it is latched. A Schmitt-Trigger mini-

mizes the effects of electrical noise.

The electrical characteristics and drive capabilities of the in-

put and output buffers are described in Section25.0.

For some pins, a direct low-impedance path is provided be-

tween the pin and an internal analog function. These are the

input pins to the A/D converter and the analog comparators.

6.1

PORT REGISTERS

Each port has an associated set of memory-mapped regis-

ters used for controlling the port and for holding the port data.

In general, there are five such registers:

— PxALT: Port alternate function register

— PxDIR: Port direction register

— PxDIN: Port data input register

— PxDOUT: Port data output register

— PxWKPU: Port weak pull-up register

In the descriptions of the ports and port registers, the lower-

case letter “x” represents the port designation, either B, C, F,

G, H, I, or L. For example, “PxDIR register” means any one

of the port direction registers: PBDIR, PCDIR, PFDIR, and so

on.

All of the port registers are byte-wide read/write registers, ex-

cept for the port data input registers, which are read-only reg-

isters. Each register bit controls the function of the

corresponding port pin. For example, PFDIR.2 (bit 2 of the

PFDIR register) controls the operation of port pin PF2.

Figure 1.

I/O Pin Functional Diagram

Direction

Data Out

{

Direction

{

Weak pull-up

{

Alternate Data Input

Weak pull-up

Data Out

Alt Device Data Output

Alt

Alt Device Direction

Data In Read Strobe

Alt

Data Input

Alt

Alternate Function

enable

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