1. General Purpose I/O

2. PORTS
Ports provide an interface between the processor and the outside world and support variety of I/O functions.

3. 68HC11 Ports
PORT A
PORT B
PORT C
PORT D
PORT E

4. 68HC11 Microcontroller

5. PORT B in single-chip mode
General purpose output port (8 pins)
Data is output to port B via port B register (PORTB)
PORTB is located in the 64-byte register block
PORTB address is $1004 (THRSIM simulation) or $04 (68HC11 MCU)

6. Programming Port B
Write a program to make port B high ORG $0200 LDAA #$FF STAA $1004 Write a program to make PB0-PB2 high and the rest low LDAA #%

7. Port B in Expanded Mode
Port B pins are used as the upper byte of the 16-bit external address bus (ADDR8-ADDR15)

8. Port C In Single-Chip mode
8 bit general purpose bidirectional port
It consist of an 8-bit data register (PORTC). $1003 or $03.
It consist of an 8-bit data direction register (DDRC). $1007 or $07.

9. DDRC
Each bit in the DDRC controls the direction of the corresponding bit in the port c register
Ex. Make port C input, read data from port C and store it in $0400.
ORG $0200
CLR $1007 ; Port c input
LDAA $1003 ; read input
STAA $0400

10. More examples
Ex. Make port C output, make all output high. ORG $0200 LDAA #$FF STAA $1007 STAA $1003

11. Port C in Expanded mode
Port C pins are used as the lower byte of the 16-bit external address bus (ADDR0-ADDR7) and external data bus (D0-D7)

12. Bit level operation instructions
BSET
BCLR
BITA
BITB
BRSET
BRCLR

13. PORT A 8-BIT general purpose I/O port.
PA4-PA6 are outputs or output compare pins.
PA0-PA2 are inputs or input-edge-detected pins.
PA3 & PA7 are programmable I/O. These two lines are controlled by two data direction control bits. PACTL ($1026 or $26)
Port A data register allows data to flow in and out of the port. ($1000 or$00)
Bit 6 in PACTL register is used to switch port A function from general purpose I/O to input capture and output compare operation.
PAEN = 0 GPIO, PAEN = 1 input capture/output compare

14. Port D 8-bit I/O port. PD0 –PD5 are programmable I/O.
DDRD ($1009 or $09) controls the direction of the I/O.
Port D data register ($1008 or $08).
PD0 and PD1 are used for serial transmission.
PD6 and PD7 are used in Multiplexed mode for AS and RW signals.