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Chapter 15. Registers Page 15-67
15.10.6 USB Frame Count Low
Figure 15-68. USB Frame Count Low
Bit 7-0 FC7:0 Low Byte for USB Frame Count
Every millisecond the host sends a SOF token indicating Start Of Frame, along with an 11-bit
incrementing frame count. The EZ-USB FX2 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. If
the USB core detects a missing or garbled SOF, it generates an internal SOF and increments
USBFRAMEL-USBRAMEH.
15.10.7 USB Microframe Count
Figure 15-69. USB Microframe Count
Bit 2-0 MF2:0 Last Occurring Microframe
MICROFRAME contains a count 0-7 which indicates which of the 8 125-microsecond microf-
rames last occurred. This register is active only when FX2 is operating at high speed (480
Mbits/sec).
USBFRAMEL USB Frame Count LOW E685
b7 b6 b5 b4 b3 b2 b1 b0
FC7 FC6 FC5 FC4 FC3 FC2 FC1 FC0
R R R R R R R R
x x x x x x x x
MICROFRAME USB Microframe Count, 0-7 E686
b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0 0 MF2 MF1 MF0
R R R R R R R R
0 0 0 0 0 x x x
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