1.15 Interrupts
The EZ-USB enhanced 8051 adds seven interrupt sources to the standard 8051 interrupt
system. Three of the added interrupts are used internally, and the others are available on
device pins. INT2 is used for all USB interrupts. INT3 is used by the I2C interface. A
third interrupt is used for remote wakeup indication.
The EZ-USB core automatically supplies jump vectors (Autovectors) for its USB inter-
rupts to save the 8051 from having to test bits to determine the source of the interrupt.
Each BULK/CONTROL/INTERRUPT endpoint has its own vector, so when an endpoint
requires service, the proper interrupt service routine is automatically invoked. The 8051
services all isochronous endpoints in response to a SOF (Start Of Frame) interrupt request.
Chapter 9, "EZ-USB Interrupts" describes the EZ-USB interrupt system.
1.16 Reset and Power Management
The EZ-USB chip contains four resets:
•
•
•
•
Power-On-Reset (POR)
USB bus reset
8051 reset
USB Disconnect/Re-connect
The functions of the various EZ-USB resets are described in Chapter 10, "EZ-USB
Resets."
A USB peripheral may be put into a low power state when the host signals a suspend oper-
ation. The Universal Serial Bus Specification Version 1.1 states that a bus powered device
cannot draw more than 500 uA of current from the Vcc wire while in suspend. The EZ-
USB chip contains logic to turn off its internal oscillator and enter a sleep state. A special
interrupt, triggered by a wakeup pin or wakeup signaling on the USB bus, starts the oscil-
lator and interrupts the 8051 to resume operation.
Low power operation is described in Chapter 11, "EZ-USB Power Management."
EZ-USB TRM v1.9
Chapter 1. Introducing EZ-USB
Page 1-15
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