Motorola DSP96002 - Manual (Page 778)

D-26 DSP96002 USER’S MANUAL MOTOROLA
Figure D-13. The Exponent Adder
M1 M2
ED
D
11 Bits
11 Bits
11 Bits
Add exponents
and subtract bias
S1 S2
provide an initial approximation to 1/x and sqrt(1/x), as is described in Appendix A.
D.1.5.5 Controller and Arbtrator Unit
The controller and arbitrator (CA) unit supplies control signals to the processing units of the data ALU and
register file, and is responsible for the full implementation of the IEEE standard. Its operation is determined
by the flush-to-zero (FZ) bit in the status register (SR), which determines whether or not denormalized num-
bers are treated as defined by the standard. In the flush-to-zero mode, all denormalized input operands are
treated as zeros (although their original contents are preserved), and denormalized results are set equal to
zero ("flushed-to-zero"). In the flush-to-zero mode, no additional cycles are required for the normalization of
denormalized numbers as they are treated as zeros. In the IEEE mode, the standard for treatment of de-
normalized numbers is correctly and fully implemented. However, operations on denormalized numbers can
not be performed in a single instruction cycle, except for operations done in the floating point adder when
the operand is a denormalized number in SEP. The controller and arbitrator is responsible for providing the
correct sequence that deals with such situations.
When denormalized numbers are detected as input operands in IEEE mode, the CA unit adds one extra
cycle for entering the IEEE mode procedure. Next, one additional cycle is added for each denormalized in-
put operand. These cycles are used to normalize the input operand. The original value of the operand in the
source register is not affected. During the IEEE mode procedure all activity of the chip is suspended until
the input operands have been normalized. When denormalized output results are detected, the IEEE mode
procedure is entered (one additional instruction cycle) and each result is again normalized (another cycle).