On Jan 6, 17:58, Tom Leffingwell wrote: The smaller switch, S1, controls the vector. S1-1 to S1-8 correspond to bits 9 to 2 of the vector, respectively. ON sets a '1' in the corresponding bit position. Default is OFF, OFF, OFF, ON, OFF, ON, OFF, ON = 00010101 which gives a vector of 000124. The larger switch, S2, controls the base address. The DRV11-B has 5 registers, with factory-standard addresses as follows: WCR Word Count Register 772410 BAR Bus Address Register 772412 CSR Control and Status Register 772414 IDBR Input Data Buffer Register 772416 ODBR Output Data Buffer Register 772420 Note that the CSR is not the first address. S2-1 to S2-10 correspond to bits 12 to 3 in the base address. ON sets a '1' in the corresponding bit position. Bits 15-13 are fixed at '1'. Default is ON, OFF, ON, OFF, ON, OFF, OFF, OFF, OFF, ON = 1010100001, which gives 172410 (corresponds to 772410 with 18-bit addressing). -- Pete Peter Turnbull Network Manager University of York