# Autodecrement Mode
The autodecrement addressing mode decreases the value in the specified register
by the number of bytes indicated by the VAX data type, and then the register is
used as a pointer to memory to access the VAX data type. It is identified by
byte values 0x70 through 0x7E with the low nibble indicating which register is
used. 0x7F (which would use the PC) is unpredictable.