Replaceable print material supply cartridges for printers are disclosed herein. An example replaceable print material supply cartridge includes logic circuitry that is to determine a position of the replaceable print material supply cartridge by initiating a first voltage on a data contact during a time period, monitoring a timer without reference to a clock signal at a clock contact from a serial data bus, and maintaining a first voltage on the data contact for a duration of time. After expiration of the duration, the logic circuitry is to cause the data contact to assume a second voltage, different than the first voltage, and the logic circuitry is to read data from the memory and cause transmission of a data signal via the serial data bus interface.