MC68HC05C9A Datasheet, PDF (41/124 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 7
Input/Output Ports
7.1 Introduction
This section briefly describes the 31 input/output (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 register
before writing a 1 to the corresponding data direction register.
7.2 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 register are indeterminate at initial power-up and must be initialized by user software. Reset does
not affect the data registers, but clears the data direction registers, thereby returning the ports to inputs.
Writing a 1 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.
DATA DIRECTION
REGISTER BIT
INTERNAL
HC05
CONNECTIONS
LATCHED OUTPUT
DATA BIT
I/O
OUTPUT
PIN
INPUT
REG.
BIT
INPUT
I/O
Figure 7-1. Port A I/O Circuit
MC68HC05C9A Advance Information Data Sheet, Rev. 5.1
Freescale Semiconductor
41