USB Host Controller Registers
14-12
Table 14–3. HC Operating Mode Register (HcControl) (Continued)
Bit
Reset
Value
Type
Description
Value
Name
3
IE
Isochronous enable
R/W
0
0
Enables processing of isochronous EDs.
1
Isochronous EDs are not processed. The USB host
controller checks this bit every time it finds an
isochronous ED in the periodic list.
When this bit is written to 1, processing of isochronous
EDs might not occur in the current frame but is enabled
in the next frame.
2
PLE
Periodic list enable
R/W
0
0
The periodic ED lists are not processed. When written
to 0, periodic list processing is disabled beginning with
the next frame.
1
Enables processing of the periodic ED lists. When
written to 1, periodic list processing begins in the next
frame.
1–0
CBSR
Control/bulk service ratio
Specifies the ratio between control and bulk EDs
processed in a frame.
R/W
00
00
One control ED per bulk ED
01
Two control EDs per bulk ED
10
Three control EDs per bulk ED
11
Four control EDs per bulk ED