Patent ID: 7054771

Claim:
A data communications system of a type that generates and interprets data signals by comparing them to one or more reference voltages, the communications system comprising: a transmitting device comprising: a first current output line; a second current output line; a first current driver that regulates drive current on the first current output line to produce high and low line voltages thereon; a second current driver that regulates drive current on the second current output line to produce high and low line voltages thereon; a variable voltage divider that divides a voltage differential between the high and low line voltages to obtain an intermediate voltage that is a dynamically programmable fraction between the high and low line voltages; a current control register that controls the drive current outputs of the first and second current drivers during normal operation; an asymmetry control register that sets the dynamically programmable fraction to adjust the variable voltage divider during calibration operations; and an up/down counter that controls the drive current outputs of the first and second current drivers during the calibration operations; and first and second receiving devices comprising: first and second receivers, respectively, that are respectively coupled to the first and second current output lines of the transmitting device; wherein at least one receiver reference voltage at the first and second receivers is varied to find high and low receiver reference voltages at which data errors do not occur while the up/down counter and the asymmetry control register are used to vary the drive currents on the first and second current output lines.