The LAMPF Microprogrammed Branch Driver (MBD) is described from a programmer's point of view, and a set of macroinstructions implemented in the PDP- 11 MACRO assembler, suitable for writing programs for it, is given. The MBD is a small, special-purpose, stored-program processor intended to serve as an interface between a CAMAC branch and a Digital Equipment Corporation PDP-11. (auth)