Figure 5-4.—Example of instruction translation and execution circuitry.
STATUS INDICATING REGISTERS. —The
CPU must have some way to monitor the status of the
computer’s internal operations. The name of these
register or registers may differ between computers, but
the general functions performed are the same. Some of
the most common names are as follows:
Condition code
Status and control
Program status
Active status
Flag
These registers use the condition of individual
bits in the register to indicate the status of opera-
tions in the computer (fig. 5-5). Within the register,
individual and sometimes groups of bits (2 or 3
bits) are hardwired to the computer logic. The 1 or 0
value in each bit position indicates the status of a
particular activity or special function of the com-
puter.
The specific activities monitored by these registers
varies between computers, but consist of the following
general areas: arithmetic operation or comparison
results (carry, overflow, zero, negative, and so forth)
Figure 5-5.—Example of a status register; indication of a
program fault.
5-7
