68HC705JB3 datasheet(47/134 Pages) FREESCALE

47 / 134 page

November 5, 1998

GENERAL RELEASE SPECIFICATION

MC68HC05JB3

INPUT/OUTPUT PORTS

MOTOROLA

REV 1

7-1

SECTION 7

INPUT/OUTPUT PORTS

In normal operating mode there are 19 usable bidirectional I/O lines arranged as

one 8-bit I/O port (Port-A), one 7-bit I/O port (Port-B), and one 4-bit I/O port

(Port C). The individual bits in these ports are programmable as either inputs or

outputs under software control by the data direction registers (DDRs).

The eight port pins, PB4-PB7 and PC0-PC3, are only available on the 28-pin

version of the device.

Table 7-1 shows a summary of Port-A, Port-B, and Port-C functions.

7.1

PORT-A

Port-A is an 8-bit bi-directional port. The Port-A data register is at $0000 and the

data direction register (DDRA) is at $0004. Reset does not affect the data regis-

ters, but clears the data direction registers, thereby returning the port pins to

inputs. Writing a ‘1’ to a DDR bit sets the corresponding port bit to output mode.

All Port-A pins have programmable pull-down resistors. PA4 to PA7 each has 8mA

current sink capability.

The table below summarizes the pin conﬁgurations for Port-A.

Table 7-1. Summary of Port Pin Functions

Port Pins

Internal Resistor

Configuration

Current

Drive/Sink

Additional Features

PA0-PA3

Pull-down1

1.6mA sink

External Interrupt2

Optical Interface

PA4-PA7

8mA sink

PB0

1.6mA sink

shared with TCAP

PB1, PB2

Pull-up1

25mA sink,

open-drain

Slow Transition Output

PB4-PB7

Pull-down1

1.6mA sink

Pins available only

in 28-pin device

PC0

shared with OCMP

PC1-PC3

Notes:

A pull-up/pull-down resistor is enabled by setting the corresponding register bit to “0” and the

port pull-up/down mask option is selected.

Selected by mask option.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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