12.2.4.9 Loopback Modes

There are two loopback modes: Local loopback mode and Remote loopback mode. In the Local loopback mode, MMUART_X_TXD is set to 1. The MMUART_X_RXD, MMUART_X_DSR, MMUART_X_CTS, MMUART_X_RI, and MMUART_X_DCD inputs are disconnected. The output of the transmitter shift register is looped back into the receiver shift register. The modem control outputs (MMUART_X_DTR, MMUART_X_RTS, MMUART_X_OUT1, and MMUART_X_OUT2) are connected internally to the modem control inputs, and the modem control output pins are set as 1. The transmitted data is immediately received, allowing the Cortex-M3 processor to check the operation of the MMUART_X.

In Remote loopback mode, when a bit is received, it is sent directly out of the transmit line, bypassing the transmitter block, and disabling the receiver. Local loopback has a higher priority over Remote loopback. In Automatic echo mode, a bit is received and is sent directly out the transmit line, bypassing the transmitter block, while the receiver is still enabled. Loopback modes are enabled or disabled by making changes to the modem control register (Table 12-18).