MC68HC705P6A Datasheet, PDF (52/130 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Input/Output Ports
6.3 Port A
Port A is an 8-bit bidirectional port, which does not share any of its pins
with other subsystems (see Figure 6-1). The port A data register is
located at address $0000 and its data direction register (DDR) is located
at address $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 does clear the DDRs,
thereby setting all of the port pins to input mode. Writing a 1 to a DDR bit
sets the corresponding port pin to output mode. Port A has mask option
register enabled interrupt capability with an internal pullup device
NOTE: The keyscan (pullup/interrupt) feature available on port A is NOT
available in the ROM device, MC68HC05P6.
READ $0004
WRITE $0004
WRITE $0000
READ $0000
INTERNAL HC05
DATA BUS
RESET
(RST)
DATA DIRECTION
REGISTER BIT
DATA
REGISTER BIT
V_DD
PULLUP MASK
OPTION REGISTER
I/O
OUTPUT
PIN
Figure 6-1. Port A I/O and Interrupt Circuitry
TO IRQ
INTERRUPT SYSTEM
Advance Information
52
Input/Output Ports
MC68HC705P6A — Rev. 2.0
MOTOROLA