2. 3. Microprogram sequencing
• Microprogram is simple because std
software technique can be used.
• However, two major disadvantages may be
answered by this method.
• Separate microroutine for each machine
instruction cause large no of
microinstruction and large control store.
3. Contd.,
• Most machine instruction involve several
addressing mode.
• Many instruction of a processor have
different combinations of addressing modes.
• A separate microroutine for each of these
combinations would produce considerable
duplication of common parts.
4. • We should organize the microroutine so that
many common parts would share as
possible.
• [when it arise execution time is longer
because it takes more time to carry out the
required branches]
5. Example
–Add src, dst
the source operand can be specified in the
following addressing modes
1. Register
2. Auto increment
3. Auto decrement
4. indexed
8. 5. Prefetching microinstructions
One major drawback of microprogrammed
control is slower operating speed.bcoz of
fetching every micoinstruction from CS.
Prefetching of microinstruction facing some
operational difficulties that it must consider the
status flags and result of currently being
executed microinstruction.
Some time straight forward prefetches a wrong
microinstruction. Thus, the fetch must be
repeated with the correct address and it will
require more complex hardware.
9. 6.Emulation - Duplicate
• Additional instruction set.-Emulate the
function of one system to another so the
emulated machine reassembles the behavior
of real system.
• Programs written in the machine language
of M2 machine can then be run on computer
M1.
10. 6.Emulation - Duplicate
• Additional instruction set.-Emulate the
function of one system to another so the
emulated machine reassembles the behavior
of real system.
• Programs written in the machine language
of M2 machine can then be run on computer
M1.