Bit 2-0:
EP
Select endpoint
The 8051 sets these bits to select an endpoint prior to setting its R or S bit. Valid values
are 0-7 to correspond to bulk endpoints IN0-IN7 and OUT0-OUT7.
USBFRAMEL
USB Frame Count Low
7FD8
b7
b6
b5
b4
b3
b2
b1
b0
FC7
FC6
FC5
FC4
FC3
FC2
FC1
FC0
R
x
R
x
R
x
R
x
R
x
R
x
R
x
R
x
USBFRAMEH
USB Frame Count High
7FD9
b7
b6
b5
b4
b3
b2
b1
b0
0
0
0
0
0
FC10
FC9
FC8
R
x
R
x
R
x
R
x
R
x
R
x
R
x
R
x
Figure 12-33. USB Frame Count High/Low Registers
Every millisecond the host sends a SOF token indicating “Start Of Frame,” along with an
11-bit incrementing frame count. The EZ-USB copies the frame count into these registers
at every SOF. One use of the frame count is to respond to the USB SYNC_FRAME
request (Chapter 7, "EZ-USB Endpoint Zero").
If the USB core detects a missing or garbled SOF, it generates an internal SOF and incre-
ments USBFRAMEL-USBRAMEH.
EZ-USB TRM v1.9
Chapter 12. EZ-USB Registers
Page 12-41
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