The MAX1240 has an internal 2.5V reference, while the MAX1241 requires an external reference. The MAX1241 accepts signals from 0V to VREF, and the reference input range includes the positive supply rail. An external clock accesses data from the 3-wire interface, which connects directly to standard microcontroller I/O ports. The interface is compatible with SPITM, QSPITM, and MICROWIRETM.