The trs80gp Setup menu provides all the functionality of the DT-1 SET-UP screen in a somewhat more descriptive format. It will also change the SET-UP screen if you're in it so you can learn the cryptic settings. Use Setup → Duplex → Half to put the DT-1 into a mode where you will see each character you type. If you're feeling really adventurous type <ESC>G2Blinking<ESC>G0text to see some blinking text.
trs80gp's DT-1 emulation is missing a few features of the original. There's no way to attach a printer, not all input keycodes can be generated, there's no half-intensity text mode and no beep. If you have a real DT-1 please get in touch as a few tests could go along way to implementing the missing features.