68HC05CT4 datasheet(57/142 Pages) FREESCALE

57 / 142 page

Parallel Input/Output (I/O)

Port D

MC68HC05CT4 — Rev. 2.0

General Release Specification

Parallel Input/Output (I/O)

7.6 Port D

Port D is a 7-bit bidirectional port. Two of its pins are shared with the SSI

subsystem, four are shared with the comparators, and one is shared with

the timer. During reset, all seven bits become valid input ports because

all special function output drivers associated with the timer and SSI

subsystems are disabled.

7.7 Input/Output Port Pin Programming

Port pins may be programmed as inputs or outputs under software

control. The direction of the pins is determined by the state of the

corresponding bit in the port data direction register (DDR). Each I/O port

has an associated DDR. Any I/O port pin is configured as an output if its

corresponding DDR bit is set to a logic one. A pin is configured as an

input if its corresponding DDR bit is cleared to a logic 0.

At power-on or reset, all DDRs are cleared, which configures all pins as

inputs. The data direction registers are capable of being written to or

read by the processor. During the programmed output state, a read of

the data register actually reads the value of the output data latch and not

the I/O pin.

Refer to Table 7-1 and to Figure 7-2 for additional information.

Table 7-1. I/O PIn Functions

R/W

DDR

I/O Pin Functions

The I/O pin is in input mode. Data is written into the output

data latch.

Data is written into the output data latch and output to the

I/O pin.

The state of the I/O pin is read.

The I/O pin is in an output mode. The output data latch is

read.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

68HC05CT4 Datasheet(PDF) 57 Page - Freescale Semiconductor, Inc