SMSC USB2640i - Manual (Page 43)

Ultra Fast USB 2.0 Multi-Format Flash Media Controller/USB Hub Combo
SMSC USB2640/USB2641 43 Revision 2.0 (10-03-08)
DATASHEET
7.3.3.28 EFh: Boost_Up
7.3.3.29 F0h: Boost_3:0
BIT
NUMBER 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 (one
example would be Test J/K levels), OEM should use a ‘00’ value
unless specific implementation issues require additional signal
boosting to correct for degraded USB signalling levels.
BIT
NUMBER BIT NAME DESCRIPTION
7:6 Reserved Always reads ‘0’.
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 (one
example would be Test J/K levels), OEM should use a ‘00’ value
unless specific implementation issues require additional signal
boosting to correct for degraded USB signalling levels.
1:0 Reserved Always reads ‘0’.