97
12. P
ARALLEL
P
ORT
E
12.1 Overview
Parallel Port E is a byte-wide port with each bit programmable for data direction and drive
level. These are simple inputs and outputs controlled and reported in the Port E Data
Register (PEDR).
All of the Parallel Port E pins have alternate output functions, and all of them can be used
as inputs to various on-chip peripherals.
When used as outputs, the Parallel Port E bits are buffered, with the data written to PEDR
transferred to the output pins on a selected timing edge. Either the peripheral clock or the
outputs of Timer A1, Timer B1, or Timer B2 can be used for this function, with each nib-
ble of the port having a separate select field to control this timing. Each bit can either be
programmed as open-drain or driven high and low.
Because of the buffered nature of Parallel Port E, using a read-modify-write type of opera-
tion can lead to old data being written to PEDR. To alleviate this potential problem, each
bit of the port can be written individually using a separate address for each bit.
Bit 7 of Parallel Port E is used as the default chip select input for the slave port when the
slave port is enabled, either for parallel bootstrap or under program control.
Table 12-1. Parallel Port E Pin Alternate Output Functions
Pin Name
Alt Out 0
Alt Out 1
Alt Out 2
Alt Out 3
PE7
I7
/ACT
PWM3
SCLKC
PE6
I6
—
PWM2
TXE
PE5
I5
/LINK
PWM1
RCLKE
PE4
I4
/A0
PWM0
TCLKE
PE3
I3
A23
TIMER C3
SCLKD
PE2
I2
A22
TIMER C2
TXF
PE1
I1
A21
TIMER C1
RCLKF
PE0
I0
A20
TIMER C0
TCLKF
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