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2010 - 2015 Microchip Technology Inc. DS00001692C-page 29
USB251xB/xBi
5.1.28 REGISTER F8H: BOOST_4:0
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)
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 sig-
naling levels.
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.