THVD4431 provides full path diagnostic loopback modes for both RS-232 and RS-485. These modes internally short the bus outputs to the bus inputs (shown in Figure 2-3 and Figure 2-4). So, if the digital logic data is toggled by MCU, data is translated to bus (as analog bus signals) and is reflected back on logic buffer output. This enables MCU to detect bus side shorts (due to shorted connector or cable) by comparing logic input and logic output.

While the Maxlinear XR34350 and SP339E/B multiprotocol transceivers also provide diagnostic loopback for RS-232, the transceivers provide logic loopback by connecting logic driver inputs to logic receiver outputs bypassing the analog driver and receiver circuitry. The analog/bus pins are internally disconnected in this mode. As a result, XR34350/SP339 devices are unable to detect bus side faults. Additionally, these devices do not have RS-485 loopback mode.

Clearly, for safety critical applications, THVD4431 offers enhanced functionality through diagnostic loopback modes eliminating any external circuitry in place to detect cable/connector shorts.

Figure 2-3 THVD4431 in RS-232 Loopback Mode

Figure 2-4 THVD4431 in RS-485 Loopback Mode