Datasheet

USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 2.3 (06-11-13) 36 SMSC USB251xB/xBi
DATASHEET
5.1.28 Register F8h: Boost_4:0
Note: Boost could result in non-USB compliant parameters. Therefore, a value of 00 should be
implemented unless specific implementation issues require additional signal boosting to correct
for degraded USB signalling levels.
5.1.29 Register FAh: Port Swap
BIT
NUMBER BIT NAME DESCRIPTION
7:6 BOOST_IOUT_4 USB electrical signaling drive strength boost bit for downstream port 4.
00 : normal electrical drive strength - no boost
01 : elevated electrical drive strength - low (~4% boost)
10 : elevated electrical drive strength - medium (~ 8% boost)
11 : elevated electrical drive strength - high (~12% boost)
5:4 BOOST_IOUT_3 USB electrical signaling drive strength boost bit for downstream port 3.
00 : normal electrical drive strength - no boost
01 : elevated electrical drive strength - low (~4% boost)
10 : elevated electrical drive strength - medium (~ 8% boost)
11 : elevated electrical drive strength - high (~12% boost)
3:2 BOOST_IOUT_2 USB electrical signaling drive strength boost bit for downstream port 2.
00 : normal electrical drive strength - no boost
01 : elevated electrical drive strength - low (~4% boost)
10 : elevated electrical drive strength - medium (~ 8% boost)
11 : elevated electrical drive strength - high (~12% boost)
1:0 BOOST_IOUT_1 USB electrical signaling drive strength boost bit for downstream port 1.
00 : normal electrical drive strength - no boost
01 : elevated electrical drive strength - low (~4% boost)
10 : elevated electrical drive strength - medium (~ 8% boost)
11 : elevated electrical drive strength - high (~12% boost)
BIT
NUMBER BIT NAME DESCRIPTION
7:0 PRTSP Port Swap: swaps the upstream USBDP/USBDM pins (USBDP_UP and
USBDM_UP) and the downstream USBDP/USBDM pins (USBDP_DN[x:1]
and USBDP_DN[x:1]) for ease of board routing to devices and connectors.
0 : USB D+ functionality is associated with the DP pin and D- functionality
is associated with the DM pin.
1 : USB D+ functionality is associated with the DM pin and D- functionality
is associated with the DP pin.
Bit 7 : rsvd
Bit 6 : rsvd
Bit 5 : rsvd
Bit 4 : controls port 4
Bit 3 : controls port 3
Bit 2 : controls port 2
Bit 1 : controls port 1
Bit 0 : when set to
1, the upstream port DP/DM is swapped.