The I²C bus operates in one of three speed modes: standard, which allows a clock frequency of up to 100 kHz; fast, which allows a clock frequency of up to 400 kHz; and high-speed mode (also called Hs mode), which allows a clock frequency of up to 3.4 MHz. The ADS1000-Q1 is fully compatible with all three modes.

No special action must be taken to use the ADS1000-Q1 in standard or fast modes, but high-speed mode must be activated. To activate high-speed mode, send a special address byte of 00001XXXb following the start condition, where the XXX bits are unique to the Hs-capable controller. This byte is called the Hs controller code. (This byte is different from normal address bytes; the low bit does not indicate read/write status.) The ADS1000-Q1 does not acknowledge this byte; the I²C specification prohibits acknowledgment of the Hs controller code. On receiving a controller code, the ADS1000-Q1 switches on the high-speed mode filters, and communicates at up to 3.4 MHz. The ADS1000-Q1 switches out of Hs mode with the next stop condition.

For more information on high-speed mode, consult the I²C specification.