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EZ-USB FX2 Technical Reference Manual
Page 6-6 EZ-USB FX2 Technical Reference Manual v2.1
The Wakeup Interrupt Service Routine clears the interrupt request flag (using the ‘bit clear’ instruc-
tion, i.e. ‘clr EICON.4’), and then executes a ‘reti’ (return from interrupt) instruction. This causes
the FX2 to continue program execution at the instruction following the one that set PCON.0 to ini-
tiate the power-down operation.
If PCON.0 is set when no Suspend condition exists (i.e., the USB is not signaling “Suspend”, and
firmware hasn’t written to the SUSPEND register), the Wakeup Interrupt will fire immediately.
6.4 USB Resume (Remote Wakeup)
Figure 6-4. USB Control and Status register
Firmware sets the SIGRSUME bit to send a remote-wakeup request to the host. To be compliant
with the USB Specification, the firmware should wait 5 milliseconds after the wakeup interrupt, set
the SIGRSUME bit, wait 10-15 milliseconds, then clear it.
Holding either WAKEUP pin in its active state (as determined by the programmed polarity) inhibits
the FX2 chip from turning off its oscillator in order to enter the ‘suspend’ state.
The Default USB Device does not support remote wakeup. This fact is reported at enumeration
time in byte 7 of the built-in Configuration Descriptor (see Appendices A and B).
6.4.1 WU2 Pin
The WU2 function shares the general-purpose I/O pin PA3. Unlike other multi-purpose I/O pins
that use configuration registers (PORTACFG, PORTBCFG and PORTCCFG) to select alternate
About the Wakeup Interrupt
The FX2 enters its idle state when it sets PCON.0 to 1. Although a standard 8051 exits the
idle state when any interrupt occurs, the FX2 supports only the Wakeup Interrupt to exit the
idle state.
USBCS USB Control and Status 7FD6
b7 b6 b5 b4 b3 b2 b1 b0
HSM - - - DISCON NOSYNSOF RENUM SIGRSUME
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