MC68HC05C8A Datasheet, PDF (37/116 Pages) Motorola, Inc – Microcontrollers

Chapter 7
Input/Output (I/O) Ports
7.1 Introduction
The MC68HC05C8A has three 8-bit input/output (I/O) ports.These 24 port pins are programmable as
either inputs or outputs under software control of the data direction registers. Port D does not have a data
direction register, and its seven pins are input only with the exception of certain serial communications
(SCI)/serial peripheral interface (SPI) functions.
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. 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.
7.3 Port B
Port B is an 8-bit bidirectional port. The port B data register is at $0001 and the data direction register
(DDR) is at $0005. 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 pin to output mode. Each
of the port B pins has a mask programmable interrupt capability. This interrupt option also enables a
pullup device when the pin is configured as an input (see Figure 7-1). The edge or edge and level
sensitivity of the IRQ pin also will pertain to the enabled port B pins via mask options. Be careful when
using port B pins that have the pullup enabled. Before switching from an output to an input, the data
should be preconditioned to a 1 to prevent an interrupt from occurring.
V_DD
V_DD
MASK OPTION
DDR BIT
IRQ
SCHMITT
TRIGGER
PB0
NORMAL PORT CIRCUITRY
AS SHOWN IN Figure 7-2
FROM ALL OTHER PORT B PINS
TO INTERRUPT
LOGIC
Figure 7-1. Port B Pullup Option
MC68HC05C8A • MC68HCL05C8A • MC68HSC05C8A Data Sheet, Rev. 5.1
Freescale Semiconductor
37