The 8051 code responds to the SUSPEND interrupt by taking the following steps:
1. Performs any necessary housekeeping such as shutting off external power-con-
suming devices.
2. Sets bit 0 of the PCON SFR (Special Function Register). This has two effects:
•
•
The 8051 enters its idle mode, which is exited by any interrupt.
The 8051 sends an internal signal to the EZ-USB core which causes it to turn
off the oscillator and PLL.
These actions put the EZ-USB chip into a low-power mode, as required by the USB Spec-
ification.
11.3 Resume
12 MHz
WAKEUP# pin
START
USB Resume
Oscillator
PLL
48 MHz
Restart
Delay
div by
2
CLK24
Signal
Resume
Resume INT
8051
(USBCS.0)
Figure 11-3. EZ-USB Resume Sequence
EZ-USB TRM v1.9
Chapter 11. EZ-USB Power Management
Page 11-3
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