SEI diagrams are built such that SUS watchdogs trip SEI watchdogs. During testing, the QUAD can be installed on one teststand while the ISI is installed on a second teststand. The connection between SUS and ISI is not necessary in this case. For convenience (no need to modify/recompile the model after every change), I added in the diagram of h1isitst.mdl a switch that disables the ISI-SUS watchdogs connection.
By default (variable at 0, case after recompiling a model without any burt restore), the ISI will read the SUS watchdog. If the variable H2:ISI-TST_SUS_WATCHDOG_DISABLE is set to one, the state of the SUS watchdog is ignored.