Texas Instruments TMS320C2XX - Manual (Page 56)

Central Arithmetic Logic Section
3-11 Central Processing Unit
3.3.3 Output Data-Scaling Shifter
The output data-scaling shifter (output shifter) has a 32-bit input connected to
the 32-bit output of the accumulator and a 16-bit output connected to the data
bus. The shifter copies all 32-bits of the accumulator and then performs a left
shift on its content; it can be shifted from zero to seven bits, as specified in the
corresponding store instruction. The upper word (SACH instruction) or lower
word (SACL instruction) of the shifter is then stored to data memory. The con-
tent of the accumulator remains unchanged.
When the output shifter performs the shift, the MSBs are lost and the LSBs are
zero filled. Figure 3–7 shows an example in which the accumulator value is
shifted left by four bits and the shifted high word is stored to data memory.
Figure 3–8 shows the same accumulator value shifted left by 6 bits and then
the shifted low word stored.
Figure 3–7. Shifting and Storing the High Word of the Accumulator
Data-memory
location
0 0 F 0 F 0 A 1
0 F 0 F 0 A 1 0
32
Output shifter
(left shift by 4 bits)
Accumulator
16
0 F 0 F
Figure 3–8. Shifting and Storing the Low Word of the Accumulator
Data-memory
location
0 0 F 0 F 0 A 1
3 C 3 C 2 8 4 0
32
Output shifter
(left shift by 6 bits)
Accumulator
16
2 8 4 0