Nanocode

The sub-code of a two-stage or multi-stage microprogram control unit that is integrated into the microcode is called nanocode . A completely horizontally coded micro-instruction does not contain any nano-instructions, but is composed entirely of control bits (so-called pico instructions). The nanocode is associated with the vertical or diagonal micro-instruction coding.

The use of the nanocode allows the compression of horizontally encoded microcode by referencing the microinstruction parts that make up the nanoprogram . In this way, the word length of the microinstruction can be shortened and the microcode allocation in the microprogram memory can be used more effectively. With 8 bits, for example, 256 control commands can be addressed in nanocode, which enables subsequent horizontal microcode processing of a defined bit length in the sense of a subroutine processing. Before it is executed, the nanocode is interpreted by decoding circuits / multiplexers, converted into horizontal microcode with the appropriate bit length and fed to the microprogram control unit.

For example, microprocessors of type MC68000 process nanocode .

literature

• R. Hoffmann: Computer design: arithmetic units, microprogramming, RISC , 3rd edition. Oldenbourg, Munich 1993, ISBN 978-3-486-22174-9 (especially Chapter 5: Microprogramming, pp. 159–240)
• W. Oberschelp, G. Vossen: Computer structure and computer structures , 10th edition. Oldenbourg, Munich 2006, ISBN 978-3-486-57849-2
• H. Malz: Computer architecture , 2nd edition. Vieweg + Teubner, 2004, ISBN 978-3-528-13379-5
• Th. Beierlein, O. Hagenbruch: Pocket book on microprocessor technology , 3rd edition, Hanser Verlag, 2004, ISBN 978-3-446-22072-0
• WK Giloi: Computer architecture , 2nd edition, Springer, 1993, ISBN 978-3-540-56355-6