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PIC18F2525 Datasheet(PDF) 91 Page - Microchip Technology |
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PIC18F2525 Datasheet(HTML) 91 Page - Microchip Technology |
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91 / 412 page  © 2008 Microchip Technology Inc. DS39626E-page 89 PIC18F2525/2620/4525/4620 8.0 8 x 8 HARDWARE MULTIPLIER 8.1 Introduction All PIC18 devices include an 8 x 8 hardware multiplier as part of the ALU. The multiplier performs an unsigned operation and yields a 16-bit result that is stored in the product register pair, PRODH:PRODL. The multiplier’s operation does not affect any flags in the STATUS register. Making multiplication a hardware operation allows it to be completed in a single instruction cycle. This has the advantages of higher computational throughput and reduced code size for multiplication algorithms and allows the PIC18 devices to be used in many applica- tions previously reserved for digital signal processors. A comparison of various hardware and software multiply operations, along with the savings in memory and execution time, is shown in Table 8-1. 8.2 Operation Example 8-1 shows the instruction sequence for an 8 x 8 unsigned multiplication. Only one instruction is required when one of the arguments is already loaded in the WREG register. Example 8-2 shows the sequence to do an 8 x 8 signed multiplication. To account for the sign bits of the arguments, each argument’s Most Significant bit (MSb) is tested and the appropriate subtractions are done. EXAMPLE 8-1: 8 x 8 UNSIGNED MULTIPLY ROUTINE EXAMPLE 8-2: 8 x 8 SIGNED MULTIPLY ROUTINE TABLE 8-1: PERFORMANCE COMPARISON FOR VARIOUS MULTIPLY OPERATIONS MOVF ARG1, W ; MULWF ARG2 ; ARG1 * ARG2 -> ; PRODH:PRODL MOVF ARG1, W MULWF ARG2 ; ARG1 * ARG2 -> ; PRODH:PRODL BTFSC ARG2, SB ; Test Sign Bit SUBWF PRODH, F ; PRODH = PRODH ; - ARG1 MOVF ARG2, W BTFSC ARG1, SB ; Test Sign Bit SUBWF PRODH, F ; PRODH = PRODH ; - ARG2 Routine Multiply Method Program Memory (Words) Cycles (Max) Time @ 40 MHz @ 10 MHz @ 4 MHz 8 x 8 unsigned Without hardware multiply 13 69 6.9 μs27.6 μs69 μs Hardware multiply 1 1 100 ns 400 ns 1 μs 8 x 8 signed Without hardware multiply 33 91 9.1 μs36.4 μs91 μs Hardware multiply 6 6 600 ns 2.4 μs6 μs 16 x 16 unsigned Without hardware multiply 21 242 24.2 μs96.8 μs242 μs Hardware multiply 28 28 2.8 μs 11.2 μs28 μs 16 x 16 signed Without hardware multiply 52 254 25.4 μs 102.6 μs254 μs Hardware multiply 35 40 4.0 μs16.0 μs40 μs |
Similar Part No. - PIC18F2525_08 |
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