The ACS101A is a complete controller, driver and receiver IC, supporting fullduplex asynchronous transmission from DC to 76.8kbps and synchronous data rates up to 512kbps over one optical fiber. The ACS101A also supports two additional low frequency asynchronous channels or RS-232 handshake signals, RTS, CTS, DTR and DSR. The ACS101A employs data compression and time compression techniques, affording high launch power in short bursts, leading to a low average power consumption. The advantage of this approach is that high link budgets can be achieved with inexpensive optical components. Communicating optical modems automatically maintain synchronisation with each other such that the receive phase of one modem is lined-up with the transmit phase of the other, compensating for the propagation delay presented by the link. Link lengths from zero to maximum distance are catered for automatically. In 'standard' mode, the fiber may be up to 2.5km long, or up to 5km in 'double' mode. 1