Hi, Apart from defining the bits, I wanted to define another struct variable in MDL and MDH regs. Here's what I need: struct CANMDH_Variable { //bits description Uint16 A:8; //32:39 Uint16 B:16; //55:40 Uint16 C:8; //63:56 }; union CANMDH_REG { Uint32 all; struct CANMDH_WORDS word; struct CANMDH_BYTES byte; struct CANMDH_BITS bit; struct CANMDH_Variable variable; }; Similarly in MDL too. When I compile this code, it gives me the following error: Severity and Description Path Resource Location Creation Time Id run placement fails for object "ECanaMboxesFile", size 0x180 (page 1). Available ranges: ECANA_MBOX size: 0x100 unused: 0x100 max hole: 0x100 Example_28335_Flash line 0 1304601263380 764