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High Speed Inter-Chip USB 2.0 Hub and Flash Media Controller
Datasheet
Revision 1.0 (06-01-09) 46 SMSC USB4640/USB4640i
DATASHEET
8.4.4.18 EFh: Boost_Up
8.4.4.19 F0h: Boost_3:0
BIT NAME DESCRIPTION
7:2 Reserved Reserved
1:0 BOOST_IOUT USB electrical signaling drive strength boost bit for the upstream port ‘A’.
‘00’ = Normal electrical drive strength = No boost
‘01’ = Elevated electrical drive strength = Low (approximately 4% boost)
‘10’ = Elevated electrical drive strength = Medium (approximately 8% boost)
‘11’ = Elevated electrical drive strength = High (approximately 12% boost)
Note: “Boost” could result in non-USB compliant parameters. OEM
should use a ‘00’ value unless specific implementation issues
require additional signal boosting to correct for degraded USB
signaling levels.
BIT NAME DESCRIPTION
7:6 Reserved Reserved
5:4 BOOST_IOUT_3 Upstream USB electrical signaling drive strength boost bit for downstream
port ‘3’.
‘00’ = Normal electrical drive strength = No boost
‘01’ = Elevated electrical drive strength = Low (approximately 4% boost)
‘10’ = Elevated electrical drive strength = Medium (approximately 8% boost)
‘11’ = Elevated electrical drive strength = High (approximately 12% boost)
3:2 BOOST_IOUT_2 Upstream USB electrical signaling drive strength boost bit for downstream
port ‘2’.
‘00’ = Normal electrical drive strength = No boost
‘01’ = Elevated electrical drive strength = Low (approximately 4% boost)
‘10’ = Elevated electrical drive strength = Medium (approximately 8% boost)
‘11’ = Elevated electrical drive strength = High (approximately 12% boost)
Note: “Boost” could result in non-USB Compliant parameters. OEM
should use a ‘00’ value unless specific implementation issues
require additional signal boosting to correct for degraded USB
signaling levels.
1:0 Reserved Always reads ‘0’.