There should be no requirement to setup the TNT to receive the DEC message. There are probably 3 scenarios that could be going wrong:
1) You are trying to send an SDC to the device without first sending the listen address. When peforming a selected device clear (0x04), the command must be preceeded by MLA. You can test this theory out by using DCL (0x14). This device clear is sent to all devices at the same time. Both of these shoulc cause ISR1[DEC] to set.
2) You could have configured the ISR interrupt registers for non-static mode (the AUXRI[SISB] bit is clear). When this occurs, the ISR registers are cleared when they are read. If this is the case and your ISR is not handing all interrupts, one may be lost. For example, if the controller sends you MLA,
SDC you will actually have two interrupts pending, ISR2[ADSC] (addressing change) and ISR1[DEC] (device clear). If you read both ISRs but only handle the ADSC interrupt, you will have "lost" the device clear interrupt.
3) You can validate that you have your device connected up correctly. Depending on the listen address you have chosen (i.e., PAD1), to receive your listen and/or talk address, you only need to use a subset of the data lines. If you have corruption in DIO3 (DIO lines go from 8-1, not 7-0), you would get your talk address and listen address, but not a device clear.
Hope this gives you some places too look.
