Operation If Gpion And Gpiox Are Different Pins - Intel PXA27 Series Design Manual

The 5.0 V to 3.3 V voltage divider is required since the PXA27x processor GPIO pins cannot
exceed 3.3 V. This voltage divider is implemented in a number of ways:
•
The most robust and expensive solution is to use a MAX6348 (or equivalent) Power-On-Reset
device. This solution produces a very clean signal edge and minimizes signal bounce.
•
A more inexpensive solution is to use a 3.3 V line buffer with 5.0 V tolerant inputs. This
solution does not reduce signal bounce, thus software must compensate by reading the GPIO
signal after it stabilizes.
•
Another solution is to implement a signal bounce minimization circuit, that, is 5.0 V tolerant,
but produces a 3.3 V signal to the GPIO signal.
12.4.1.1

Operation if GPIOn and GPIOx are Different Pins

See Figure 12-2
signals for USB cable detection.
Figure 12-2. Self Powered Device when GPIOn and GPIOx are Different Pins
PXA27x
Processor
USB Client
Controller
Any GPIO signal is defined as GPIOn and GPIOx; however, GPIOn must be a GPIO which brings
the PXA27x processor out of reduced power modes. Out of reset, software configures GPIOx as an
input to allow the USB D+ signal to float. GPIOn is configured as an input and programmed to
cause an interrupt whenever a rising or falling edge is detected. Software must read the GPIOn pin
when an interrupt occurs to determine if a USB cable is connected or not. GPIOn is driven high
when a cable is connected and returns to a low state if the cable is disconnected. If a USB cable
connect is detected, then software enables the USB Client peripheral and drives the GPIOx signal
high. This results in USB D+ being pulled high using the 1.5 K Ω resistor to indicate to the host
controller that a fast USB client device is connected per the Universal Serial Bus Specification,
Revision 1.1.
®
Intel PXA27x Processor Family Design Guide
for illustration of a self-powered USB Client device using two different GPIO
GPIOn
GPIOx
0 Ohm
USBC_P
0 Ohm
USBC_N
Note 1: Some designs use the internal pull-up resistor.
3.3V 5V
Board
1.5K
Ground
Ohm
Note 1
'USB Client Controller
USB Client
Cable
Connector
1
VBUS (+5V)
4
GND
3
USB D+
2
USB D-
USBC_002_P2
II:12-3