mc68hc705c9a Freescale Semiconductor, Inc, mc68hc705c9a Datasheet - Page 47

• Manufacturer Part Number: mc68hc705c9a
• Description: M68hc05 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 7
Input/Output (I/O) 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.
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 powerup 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
Freescale Semiconductor
Figure
To avoid a glitch on the output pins, write data to the I/O port data register
before writing a one to the corresponding data direction register.
CONNECTIONS
INTERNAL
HC05
7-1.
MC68HC05C9A Advance Information Data Sheet, Rev. 4.1
LATCHED OUTPUT
DATA DIRECTION
REGISTER BIT
Figure 7-1. Port A I/O Circuit
DATA BIT
NOTE
INPUT
REG
BIT
INPUT
I/O
OUTPUT
PIN
I/O
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