mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 106

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Parallel Input/Output Control
function has priority such that if both the digital and analog functions are enabled, the analog function
controls the pin.
Write to the port data register before changing the direction of a port pin to become an output. This ensures
that the pin will not be driven momentarily with an old data value that happened to be in the port data
register.
6.2
A set of high-page registers are used to control pullups, slew rate, and drive strength for the pins. They
may also be used in conjunction with the peripheral functions on these pins. These registers are associated
with the parallel I/O ports, but operate independently of the parallel I/O registers.
6.2.1
An internal pullup device can be enabled for each port pin by setting the corresponding bit in the pullup
enable register (PTxPEn). The pullup device is disabled if the pin is configured as an output by the parallel
I/O control logic or any shared peripheral function regardless of the state of the corresponding pullup
enable register bit. The pullup device is also disabled if the pin is controlled by an analog function.
6.2.2
Slew rate control can be enabled for each port pin by setting the corresponding bit in the slew rate control
register (PTxSEn). When enabled, slew control limits the rate at which an output can transition in order to
reduce EMC emissions. Slew rate control has no effect on pins that are configured as inputs.
6-2
Pullup, Slew Rate, and Drive Strength
Port Internal Pullup Enable
Port Slew Rate Enable
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
Data Direction Control
Port Read
Port Data Register
BUSCLK
Data
Figure 6-1. Classic Parallel I/O Block Diagram
PTxDDn
D
D
PTxDn
Q
Q
Output Enable
1
0
Synchronizer
Output Data
Input Data
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