MC9S08DN60_08 Datasheet, PDF (81/356 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 6 Parallel Input/Output Control
An output pin can be selected to have high output drive strength by setting the corresponding bit in the
drive strength select register (PTxDSn). When high drive is selected, a pin is capable of sourcing and
sinking greater current. Even though every I/O pin can be selected as high drive, the user must ensure that
the total current source and sink limits for the MCU are not exceeded. Drive strength selection is intended
to affect the DC behavior of I/O pins. However, the AC behavior is also affected. High drive allows a pin
to drive a greater load with the same switching speed as a low drive enabled pin into a smaller load.
Because of this, the EMC emissions may be affected by enabling pins as high drive.
6.3 Pin Interrupts
Port A, port B, and port D pins can be configured as external interrupt inputs and as an external means of
waking the MCU from stop or wait low-power modes.
The block diagram for each port interrupt logic is shown Figure 6-2.
PTxn
1
0S
PTxPS0
PTxES0
PTxn
1
0S
PTxPSn
PTxESn
V_DD
D ^CLR Q
CK
PTxACK
RESET
BUSCLK
PTxIF
SYNCHRONIZER
PTxMOD
PORT
INTERRUPT FF
STOP ^{STOP BYPASS}
PTxIE
PTx
INTERRUPT
REQUEST
Figure 6-2. Port Interrupt Block Diagram
Writing to the PTxPSn bits in the port interrupt pin select register (PTxPS) independently enables or
disables each port pin. Each port can be configured as edge sensitive or edge and level sensitive based on
the PTxMOD bit in the port interrupt status and control register (PTxSC). Edge sensitivity can be software
programmed to be either falling or rising; the level can be either low or high. The polarity of the edge or
edge and level sensitivity is selected using the PTxESn bits in the port interrupt edge select register
(PTxES).
Synchronous logic is used to detect edges. Prior to detecting an edge, enabled port inputs must be at the
deasserted logic level. A falling edge is detected when an enabled port input signal is seen as a logic 1 (the
deasserted level) during one bus cycle and then a logic 0 (the asserted level) during the next cycle. A rising
edge is detected when the input signal is seen as a logic 0 during one bus cycle and then a logic 1 during
the next cycle.
6.3.1 Edge Only Sensitivity
A valid edge on an enabled port pin will set PTxIF in PTxSC. If PTxIE in PTxSC is set, an interrupt request
will be presented to the CPU. Clearing of PTxIF is accomplished by writing a 1 to PTxACK in PTxSC.
MC9S08DN60 Series Data Sheet, Rev 3
Freescale Semiconductor
81