The CDCDB2000 has two methods to program the states of its 20 output drivers: SMBus and SBI.

To select between SMBus and SBI interfaces, the SBEN pin is used. Pulling the SBEN to a high level enables the SBI. Pulling the SBEN pin to ground enables the SMBus interface. When SBI is enabled, the SMBus Mask registers are active. The SMBus Mask registers allow the function of the SBI shift registers to be disabled and set the each individual channel as enabled. See Figure 6-2 for a diagram of how the SMBus Mask registers and SBI shift register interact to enable or disable each output.

Figure 6-2 SMBus Mask Register and SBI Shift Register Logic