hello, I have an HMI that is slow in writting an input to the PLC.

Looking at the PLC online, when I press a button on the touch sreen it takes about a second for that bit to register on the PLC which in turn delays the output on the rung. HMI DP321 PLC DL405 both from Automation Direct. Does anyone have any suggestons.

Normally a 405 CPU is fast. What protocol is used and type of terminal.
Check the ligths on the CPU. Rx Tx. The ligth are unfortunately for all the three comm ports, so if more connected to the cpu disconeect it if possible. If you see receives and no transmits there is something wrong.
Simple check.