Table of Contents
Advertisement
Philips Semiconductors
Volume 1
8.5 GPIO usage notes
8.5.1 Example 1: sequential accesses to IOSET and IOCLR affecting the
same GPIO pin/bit
State of the output configured GPIO pin is determined by writes into the pin's port IOSET
and IOCLR registers. Last of these accesses to the IOSET/IOCLR register will determine
the final output of a pin.
In case of a code:
IO0DIR = 0x0000 0080 ;pin P0.7 configured as output
IO0CLR = 0x0000 0080 ;P0.7 goes LOW
IO0SET = 0x0000 0080 ;P0.7 goes HIGH
IO0CLR = 0x0000 0080 ;P0.7 goes LOW
pin P0.7 is configured as an output (write to IO0DIR register). After this, P0.7 output is set
to low (first write to IO0CLR register). Short high pulse follows on P0.7 (write access to
IO0SET), and the final write to IO0CLR register sets pin P0.7 back to low level.
8.5.2 Example 2: an immediate output of 0s and 1s on a GPIO port
Write access to port's IOSET followed by write to the IOCLR register results with pins
outputting 0s being slightly later then pins outputting 1s. There are systems that can
tolerate this delay of a valid output, but for some applications simultaneous output of a
binary content (mixed 0s and 1s) within a group of pins on a single GPIO port is required.
This can be accomplished by writing to the port's IOPIN register.
Following code will preserve existing output on PORT0 pins P0.[31:16] and P0.[7:0] and at
the same time set P0.[15:8] to 0xA5, regardless of the previous value of pins P0.[15:8]:
IO0PIN = (IO0PIN && 0xFFFF00FF) || 0x0000A500
The same outcome can be obtained using the fast port access.
Solution 1: using 32-bit (word) accessible fast GPIO registers
FIO0MASK = 0xFFFF00FF;
FIO0PIN = 0x0000A500;
Solution 2: using 16-bit (half-word) accessible fast GPIO registers
FIO0MASKL = 0x00FF;
FIO0PINL = 0xA500;
Solution 3: using 8-bit (byte) accessible fast GPIO registers
FIO0PIN1 = 0xA5;
User manual
Rev. 01 — 15 August 2005
UM10139
Chapter 8: GPIO
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
92
Advertisement
Table of Contents
