Hardware Reference
In-Depth Information
MAR
Memory
control
registers
To
and
from
main
memory
MDR
PC
MBR
SP
LV
Control signals
Enable onto B bus
CPP
Write C bus to register
TOS
OPC
Cbus
Bbus
H
A
B
6
N
ALU control
ALU
Z
Shifter
Shifter control
2
Figure 4-1.
The data path of the example microarchitecture used in this chapter.
registers, to which we have assigned symbolic names such as
PC
,
SP
, and
MDR
.
Though some of these names are familiar, it is important to understand that these
registers are accessible only at the microarchitecture level (by the microprogram).
They are given these names because they usually hold a value corresponding to the
variable of the same name in the ISA level architecture. Most registers can drive
