9.6
SOF Interrupt
F
C
R
C
5
S
O
F
R
N
O
Token Pkt
Figure 9-6. A Start Of Frame (SOF) Packet
USB Start of Frame interrupt requests occur every millisecond. When the EZ-USB core
receives an SOF packet, it copies the eleven-bit frame number (FRNO in Figure 9-6) into
the USBFRAMEH and USBFRAMEL registers, and activates the SOF interrupt request.
The 8051 services all isochronous endpoint data as a result of the SOF interrupt.
9.7
Suspend Interrupt
If the EZ-USB detects 3 ms of no bus activity, it activates the SUSP (Suspend) interrupt
request. A full description of Suspend-Resume signaling appears in Chapter 11, "EZ-USB
Power Management."
9.8
USB RESET Interrupt
The USB signals a bus reset by driving both D+ and D- low for at least 10 ms. When the
EZ-USB core detects the onset of USB bus reset, it activates the URES interrupt request.
9.9
Bulk Endpoint Interrupts
The remaining 16 USB interrupt requests are indexed to the 16 EZ-USB bulk endpoints.
The EZ-USB core activates a bulk interrupt request when the endpoint buffer requires ser-
vice. For an OUT endpoint, the interrupt request signifies that OUT data has been sent
from the host, validated by the EZ-USB core, and is sitting in the endpoint buffer memory.
For an IN endpoint, the interrupt request signifies that the data previously loaded by the
8051 into the IN endpoint buffer has been read and validated by the host, making the IN
endpoint buffer ready to accept new data.
EZ-USB TRM v1.9
Chapter 9. EZ-USB Interrupts
Page 9-9
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