SP306

The SP306 is a single chip device that offers both RS-422 and RS-423 serial interfaces. The device can be programmed via two control mode pins (7 and 8). In either operating mode, the SP306 provides two fullduplex channels. A loopback function is also provided for chip selftest, which connects driver outputs to receiver inputs with no external circuitry.

The RS-422 drivers convert TTL logic levels into RS-422 differential output signals. The RS-422 line driver outputs feature high source and sink current capability. The RS423 line drivers convert TTL logic levels into inverted RS-423 output signals. All line drivers are internally protected against short circuits on their outputs.

The RS-422 receivers convert the RS-422 differential input signals into noninverted TTL logic levels. Receiver input thresholds are ±200mV. The RS-422 receivers can receive input data up to 1Mbps. The RS-423 receivers convert the RS-423 input signals into inverted TTL output logic levels. The RS-423 receivers have an input threshold of ±200mV, and can receive data up to 100kbps.

A loopback test mode is provided that puts thedriver outputs into a high impedance tristatelevel, and routes the driver outputs to their associated receiver inputs. In this configuration,the signal path is noninverting from the TTL driver inputs to the receiver TTL outputs. This operating mode allows the controlling system to perform diagnostic selftest of the RS-422/RS-423 transceiver circuitry at speeds up to 3kbps.