MC68HC705C9ACFN datasheet(63/157 Pages) FREESCALE

63 / 157 page

MC68HC705C9A — Rev. 2.0

Input/Output Ports

General Release Specification — MC68HC705C9A

Section 7. Input/Output Ports

7.1 Contents

7.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

7.3

Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

7.4

Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

7.5

Port C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

7.6

Port D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

7.2 Introduction

This section briefly describes the 31 I/O lines arranged as one 7-bit and

three 8-bit ports. All of these port pins are programmable as either inputs

or outputs under software control of the data direction registers.

NOTE:

To avoid a glitch on the output pins, write data to the I/O port data

7.3 Port A

Port A is an 8-bit bidirectional port which does not share any of its pins

with other subsystems. The port A data register is at $0000 and the data

direction register (DDR) is at $0004. The contents of the port A data

user software. Reset does not affect the data registers, but clears the

data direction registers, thereby returning the ports to inputs. Writing a

one to a DDR bit sets the corresponding port bit to output mode. A block

diagram of the port logic is shown in Figure 7-1.

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