The ELM621 is a serially controlled, three bit parallel I/O port in an 8 pin package. The high level of integration employed means that very few external components are required in order to construct a fully functional circuit with this IC. The ELM621 offers several convenient features that many users will appreciate. The provision of a 16 byte buffer allows commands to be chained and executed sequentially with one key stroke. The controllable pullup resistor on the bit 3 port pin is particularly helpful when interfacing to mechanical switches, while the ability to control character echo reduces overhead while operating under computer control. Naturally, individual as well as simultaneous read, set, clear and toggle commands are also supported.