Receiver Firmware
Designer Reference Manual
DRM050 — Rev 0
44
Receiver Firmware
MOTOROLA
8.3 Remote Wakeup
The JB16 receiver supports remote wakeup function that can wake up
the host computer during USB suspend.
During suspend, the MCU will be periodically woken up by the IRQ
driven by the external RC charging and discharging circuit. The MCU
then turns on the RF circuit (both RFW-D100 and RFW-D102) for a short
period of time, detect whether a valid mouse or keyboard RF packet
arrived for waking up the host. During this short period, the IRQ will serve
for RFW-D100 interrupt events again.
If no valid packet has been detected in this period, the receiver will sleep
again. The MCU will initiate the charging and discharging cycle again
before it enters power saving mode.
The mouse or keyboard can re-transmit an RF packet again if there is no
acknowledgment from the JB16 receiver. The maximum number of such
re-transmissions can be adjusted through the MAC application interface
transmission function.
For the JB16 receiver to be able to detect the incoming packet, some
timing parameters needed to be considered.
The first is the small wakeup duration at each IRQ wakeup. For example,
if the receiver is sleeping while a packet arrives, the transmitter will send
out a second packet because there is no acknowledge from the receiver.
If the IRQ wakeup period longer than the interval between the first and
next re-transmitted packet, the re-transmitted packet can be detected by
the receiver.
Another timing is the interval between two IRQ interrupts. Consider a
single key has been pressed on the keyboard. If an IRQ wakeup
detection duty in the receiver has just elapsed before the arrival of the
first RF keyboard packet, the receiver cannot detect that packet. The
next wakeup duty will start at the next IRQ interrupt.
It can be seen that for a smaller number of re-transmission setting in the
keyboard, all re-transmission may have taken place before the next
wakeup duty start. This means the receiver will fail to detect the pressed
key and cannot wake up the host. Therefore, the interval between two
IRQ interrupts should be shorter for a relative small re-transmission
setting in the transmitter. This time interval can be adjusted by the
external RC values, C22, and R45.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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