WiFly GSX
WiFlyGSX-um.pdf 11/11/2009
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10.2
Wake on Sensor Input
SENSE 0 to 3 inputs are available to wake the module from sleep.
SENSE 0 to 3 pins have a small current source that is activated in sleep mode. This source is
approximately 100nA, and will cause the input to float up to about 1.2VDC. If SENSE1 for
example, is enabled, pulling the SENSE1 pin to GROUND will wake the device.
To enable these inputs to wake the module, use the command
set sys trigger <value>.
The
value is a bit-mapped setting. To wake on sensor pin 2, use
set sys trig 4
, for example. Setting the
value to 0 disables all sensors pins.
Sensor inputs are rated 1.2VDC maximum. You must use a resistor divider when driving a sensor pin
from the other 3V pins such as RX. A resistor divider network with a minimum of 24K in series and
10K to ground from the UART RX or CTS pin should be used.
WARNING: Under no conditions should the voltage on any sensor input exceed 1.2VDC.
Permanent damage to the module will result.
An open drain FET is a good device to tie to the SENSE pin. The threshold is about 500mV.
Additional pullup to 1.2VDC may be used if the circuit has an impedance (due to leakage current) of
less than 5Mohms (500mv / 100nA). SENSE 0 to 3 pins that are not used should be left
unconnected.
10.3
Wake on UART
When the module is in sleep mode, the UART itself is disabled. However, wake on UART can be
accomplished by connecting the SENSE1 pin to the RX data pin. (Using the appropriate divider
resistors mentioned above)
The SuRF board (RN-134) has a built in resistor divider connecting SENSE 0 and SENSE 1 to RXD
and CTS to allow waking up the module.
Note: On SuRF board rev 2 the resistor pack connecting RX and CTS signals is not correctly
connected to the sensors. To wake on UART RX place a jumper from pin 3 on the Evaluation board
header to pin 2 on the sensor header. To wake on UART CTS place a jumper from pin 10 on the
Evaluation board header to pin 3 on the sensor header.
To enable wake on RXD, use
set sys trig 1.
It should be noted that the first (or possibly multiple) byte sent into the module will likely be lost, so
the designer should take care to send a preamble byte to wake up the module before sending valid
data bytes. A better way to do this is to use the CTS input to wake the module, and wait until it is
ready to accept data. To enable this, use
set sys trig 2.
10.4
UART Receiver, RTS/CTS Hardware Flow Control
The UART receive buffer is approx. 1024 bytes, and at lower baudrates (9600, 19200) the system
can process data into the device without need for flow control.
If constant streaming of data into RX on the device is required, care should be taken to set the
comm parameters to optimize the performance. If data has a termination char, this can be used.
Also, if data has a particular frame size, this can be used.
