Recent advances in digital microfluidics have enabled lab-on-a-chip devices for DNA sequencing, immunoassays, clinical chemistry, and protein crystallization. Basic operations such as droplet dispensing, mixing, dilution, localized heating, and incubation can be carried out using a two-dimensional array of electrodes and nanoliter volumes of liquid. The number of independent input pins used to control the electrodes in such microfluidic "biochips" is an important cost-driver, especially for disposable PCB devices that are being developed for clinical and point-of-care diagnostics. However, most prior work on biochip design-automation has assumed independent control of the electrodes using a large number of input pins. Another limitation of prior work is that the mapping of control pins to electrodes is only applicable for a specific bioassay. We present a broadcast-addressing-based design technique for pin-constrained multi-functional biochips. The proposed method provides high throughput for bioassays and it reduces the number of control pins by identifying and connecting control pins with "compatible" actuation sequences. The proposed method is evaluated using a multifunctional chip designed to execute a set of multiplexed bioassays, the polymerase chain reaction, and a protein dilution assay.