Pcs 7 Tonr

Hi All. I'm using TONR timers in a CFC to time certain steps in a sequence. I want to show the time remaining on the OS (PV - ET), but can't link the TONR blocks to the OS. I decided to use a SUB_DI block to subtract ET from PV, but it won't let me interconnect between the ET and the IN of the SUB_DI block.

Can somebody please recommend how to display time left on a TONR timer on the OS. I'm using PSC7 V6 with WINCC.

Thanking you in advance.