Asynchronous (self-timed) circuits are quite natural for realizing control-intensive designs. Many such designs are of reactive nature and inherently complex due to complicated communication protocols. In these situations programmable controllers are preferable over hardwired controllers to allow design decisions to be bound late, help correct errors that may slip through the verification process, and even permit run-time modification of control algorithms to best suit the current situation. Virtually all recent work in asynchronous controller design focusses on generating hardwired controllers. In this paper, we propose an architecture for programmable asynchronous controllers in the form of a microprogrammed asynchronous "microengine". Architectures utilizing both two-phase and four-phase handshaking are proposed. The datapath structure of the asynchronous microengine is modular and easily extensible, facilitating changes during the design phase. We ensure high performance of the asynchronous microengine by exploiting concurrency between operations and employ efficient control structures. Initial results show that the proposed microengine can yield performance close to that offered by automated high-level synthesis tools targeting custom hardwired burst-mode machines for control.