| OCR Text |
Show equal. In addition, the values of control signals that are available for EQUIVALENCE are F0 = 0 and F\ = 0, since the other three combinations of Fo and F\ are occupied for AND, Exclusive-OR, and OR. These requirements can easily be added to the formula for the total differential. For example, Equation (5.1) can be extended to the following form: dF = xyF0 + xyF0 + xy(Fi + F0 Fi) + x y F0 F\. (5.3) One way to implement this equation is to add one NOR gate to the general logic function block (see Figure 5.6). The number of control lines is thus reduced from four to two at the expense of one additional NOR gate in the ALU. The speed of the modified ALU depends on the system design and can not be determined without more detailed specifications. 5.2.4 Real Time Filter The filter executes fast evaluation of Boolean expressions as a basic operation. Boolean values are obtained by comparisons between event values and constants. The comparison operations and constants are determined by the director. The filter provides also bit masking, since extracting bit fields is a common operation in monitoring. A block diagram describing the functionality of a generic filter is shown in Figure 5.7. An actual implementation can be an expanded or a restricted version Table 5.1. Control Signals to Specify the ALU Operations 127 Function F0 F1 x - y 0 0 xy 0 1 x ® y 1 0 x + y 1 1 |
