All ARM processors implement the undefined instruction space as one of the entry mechanisms for the undefined instruction exception. That is, ARM instructions with opcode[27:25] = 0b011 and opcode[4] = 0b1 are undefined on all ARM processors including the ARM9TDMI and ARM7TDMI.

ARMv4 and ARMv4T also introduce a number of instruction set extension spaces to the ARM instruction set. These are:

Instructions in these spaces are undefined, and cause an undefined instruction exception. The ARM9TDMI fully implements all the instruction set extension spaces defined in ARMv4T as undefined instructions, allowing emulation of future instruction set additions.