Microsequencer
Encyclopedia
In computer architecture
and engineering
, a sequencer or microsequencer is a part of the control unit
of a CPU
. It generates the addresses used to step through the microprogram of a control store
.
Usually the addresses are generated by some combination of a counter, a field from a microinstruction, and some subset of the instruction register
. A counter is used for the typical case, that the next microinstruction is the one to execute. A field from the microinstruction is used for jumps, or other logic.
Since CPUs implement an instruction set, it's very useful to be able to decode the instruction's bit
s directly into the sequencer, to select a set of microinstructions to perform a CPU's instructions.
Most modern CPUs are considerably more complex than this description suggests. They tend to have multiple cooperating micromachines with specialized logic to detect and handle interference between the micromachines.
Computer architecture
In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....
and engineering
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
, a sequencer or microsequencer is a part of the control unit
Control unit
A control unit in general is a central part of the machinery that controls its operation, provided that a piece of machinery is complex and organized enough to contain any such unit. One domain in which the term is specifically used is the area of computer design...
of a CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
. It generates the addresses used to step through the microprogram of a control store
Control store
A control store is the part of a CPU's control unit that stores the CPU's microprogram. It is usually accessed by a microsequencer. Early control stores were implemented as a diode-array accessed via address decoders, a form of read-only memory. This tradition dates back to the program timing...
.
Usually the addresses are generated by some combination of a counter, a field from a microinstruction, and some subset of the instruction register
Instruction register
In computing, an instruction register is the part of a CPU's control unit that stores the instruction currently being executed or decoded. In simple processors each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and ultimately...
. A counter is used for the typical case, that the next microinstruction is the one to execute. A field from the microinstruction is used for jumps, or other logic.
Since CPUs implement an instruction set, it's very useful to be able to decode the instruction's bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s directly into the sequencer, to select a set of microinstructions to perform a CPU's instructions.
Most modern CPUs are considerably more complex than this description suggests. They tend to have multiple cooperating micromachines with specialized logic to detect and handle interference between the micromachines.