Resume condition | Cypress Semiconductor
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How is the resume condition implemented?Is the wake-up pin the only way to restart the clock? Is resume interrupt driven?
There are two ways to resume normal operation,a USB bus Global Resume (USB activity detected or a Resume Signaling on the USB), or pulling the WAKEUP# pin low. Either of these conditions causes the following operations:
1) EZ-USB core restarts the oscillator.The 8051 is still in its idle state, but can now respond to interrupts.
2) EZ-USB core asserts the 8051 'resume' interrupt (this is an added interrupt in the EZ-USB 8051 core).
3) The 8051 resume ISR does whatever is needed (clear the resume IRQ bit), then executes an 'reti' instruction.
4) Code execution resumes at the instruction after the one that set the 'idle' state. EZ-USB provides a status bit to indicate how the wake-up happened -- by a USB Global Resume or by assertion of the WAKEUP# pin. If it's a remote wake-up,the 8051 generates the resume signaling pulse.