Many people use 10k or even higher to pull-up or pull-down resistors on CMOS inputs, which is generally acceptable. On some Maxim GMSL1 parts, tri-state pins are used for configuration, and these pins are internally biased midway between IOVDD and Ground. So if that is the desired level, the pin should be left open, but if a high (1) or low (0) is required, a pull-up or pull-down is needed. This resistor must overcome the internal bias on the pin in order for the level to be set correctly. The resistor value can be calculated from DC Electrical Characteristics in the datasheet, such a calculation will yield ~6K for IOVDD=3.3V and ~4K for IOVDD=1.8V Because the pin input current is voltage dependent (the datasheet value is at IOVDD=3.6V), it is safe to use 6K or less, for any IOVDD.