8.4.2 SMBus Mode

When in SMBus mode (ENSMB = 1), the VOD (output amplitude), equalization, de-emphasis, and termination disable features are all programmable on a individual lane basis, instead of grouped by A or B as in the pin mode case. Upon assertion of ENSMB, the EQx and DEMx functions revert to register control immediately. The EQx and DEMx pins are converted to AD0-AD3 SMBus address inputs. The other external control pins (MODE, RXDET and SD_TH) remain active unless their respective registers are written to and the appropriate override bit is set, in which case they are ignored until ENSMB is driven low (pin mode). On power-up and when ENSMB is driven low all registers are reset to their default state. If PWDN is asserted while ENSMB is high, the registers retain their current state.

Equalization settings accessible via the pin controls were chosen to meet the needs of most high speed applications. If additional fine tuning or adjustment is needed, additional equalization settings can be accessed via the SMBus registers. Each input has a total of 256 possible equalization settings. 4-Level Input Configuration Guidelines shows the 16 setting when the device is in pin mode. When using SMBus mode, the equalization, VOD and de-Emphasis levels are set by registers.