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UM10601
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Preliminary user manual
Rev. 1.0 — 7 November 2012
81 of 313
NXP Semiconductors
UM10601
Chapter 7: LPC800 GPIO port
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Writing to a Byte Pin register loads the output bit from the least significant bit.
•
Writing to a Word Pin register loads the output bit with the OR of all of the bits written.
(This feature follows the definition of “truth” of a multi-bit value in programming
languages.)
•
Writing to a port’s PORT register loads the output bits of all the pins written to.
•
Writing to a port’s MPORT register loads the output bits of pins identified by zeros in
corresponding positions of the port’s MASK register.
•
Writing ones to a port’s SET register sets output bits.
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Writing ones to a port’s CLR register clears output bits.
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Writing ones to a port’s NOT register toggles/complements/inverts output bits.
The state of a port’s output bits can be read from its SET register. Reading any of the
registers described in
returns the state of pins, regardless of their direction
or alternate functions.
7.7.3 Masked I/O
A port’s MASK register defines which of its pins should be accessible in its MPORT
register. Zeroes in MASK enable the corresponding pins to be read from and written to
MPORT. Ones in MASK force a pin to read as 0 and its output bit to be unaffected by
writes to MPORT. When a port’s MASK register contains all zeros, its PORT and MPORT
registers operate identically for reading and writing.
Applications in which interrupts can result in Masked GPIO operation, or in task switching
among tasks that do Masked GPIO operation, must treat code that uses the Mask register
as a protected/restricted region. This can be done by interrupt disabling or by using a
semaphore.
The simpler way to protect a block of code that uses a MASK register is to disable
interrupts before setting the MASK register, and re-enable them after the last operation
that uses the MPORT or MASK register.
More efficiently, software can dedicate a semaphore to the MASK registers, and
set/capture the semaphore controlling exclusive use of the MASK registers before setting
the MASK registers, and release the semaphore after the last operation that uses the
MPORT or MASK registers.
7.7.4 Recommended practices
The following lists some recommended uses for using the GPIO port registers:
•
For initial setup after Reset or re-initialization, write the PORT registers.
•
To change the state of one pin, write a Byte Pin or Word Pin register.
•
To change the state of multiple pins at a time, write the SET and/or CLR registers.
•
To change the state of multiple pins in a tightly controlled environment like a software
state machine, consider using the NOT register. This can require less write operations
than SET and CLR.
•
To read the state of one pin, read a Byte Pin or Word Pin register.
•
To make a decision based on multiple pins, read and mask a PORT register.
