Can I use pull-up or pull-down resistors on the digital inputs or outputs of CML devices?
A pull-up resistor is normally specified on certain pins such as the IRQN output of C-BUS or the ring detector input (RD) of telecom modems. These resistors are specified in the data sheet, with an appropriate value, and are necessary for correct device operation. IRQN outputs are open drain so that the external resistor can be varied depending on the connected load capacitance or so that internal pull-ups in the host processor can be used. The pull-up value should be low enough to give a fast, high-going edge but the trade-off is that additional current is drawn through the resistor when IRQN is asserted. Typically 100k is specified but this can be reduced if required. If the resistor is too low, then IRQN may not drive low enough to give a reliable interrupt at the processor. Operation may also become marginal and thus dependent on power supply regulation and temperature. The lowest possible value is CML device dependent and advice should be sought from Technical Support if a lower v
