| Class | Format | Key |
| b-class | 00ii iiii | i = instruction |
| t-class | 0100 ixxx | i = instruction, x = argument |
| e-class* | 0101 iiii xxxx xxxx xxxx xxxx | i = instruction, x = argument |
| v-class | 011i xxxx | i = instruction, x = argument |
| j-class | 10ix xxxx | i = instruction, x = argument |
| x-class | 11xx xxxx | x = argument |
| ext[1-13] | iiii iiii | i = instruction |
| ext1-x | 1ixx xxxx | i = instruction, x = argument (0-63) |
* stored in big-endian format