UART Test ISSUE (LOOPBACk)

If you look in the UART code created (by SOPC builder / QSYS) you might find there are two transmitters one is the real transmitter and the other is a stimulus source for rxd. You can go in and hack the connection to connect txd and rxd:-

Have a look for some lines like this:-

// assign source_rxd = rxd;

and uncomment to become

assign source_rxd = rxd;

and also find the stimulus_transmitter and disconnect the txd output

so change from

.txd (source_rxd)

to

.txd ()