How can I use the Analog JTAG port to test my metallic Tx/Rx interfaces on the LXT384?
The AT1 and AT1 pins are the analog test port input and output respectively. A voltage can be forced into any of the TTIP or RTIP pins. The voltage at the corresponding TRING or RRING pin is output at AT2. The selection is made by setting the ASR register in the JTAG interface. If the connections across the primary transformer windings are good, there should be a total impedance of approximately 2KW (DC) in the receive path (2x 1 KW). The transmit impedance will be equal to approximately two times the transmit resistor value. As an example, for E1 the impedance across the transmit path will be approximately 22W (2 x 11 W). If the impedance is much higher than the expected value, there might be an open circuit in the path (possibly caused by a bad component or soldering issue). As you can see, this feature allows testing the analog interface connections. This is something that is not possible with conventional (digital) JTAG interfaces.
