PIC18LF4420T-I/SO View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC18LF4420T-I/SO
Microchip Technology
PIC18LF4420T-I/SO Datasheet PDF : 390 Pages
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PIC18F2420/2520/4420/4520
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 argu-
ments, each argument’s Most Significant bit (MSb) is
tested and the appropriate subtractions are done.
EXAMPLE 8-1:
MOVF ARG1, W
MULWF ARG2
8 x 8 UNSIGNED
MULTIPLY ROUTINE
;
; ARG1 * ARG2 ->
; PRODH:PRODL
EXAMPLE 8-2:
MOVF ARG1, W
MULWF ARG2
BTFSC ARG2, SB
SUBWF PRODH, F
MOVF
BTFSC
SUBWF
ARG2, W
ARG1, SB
PRODH, F
8 x 8 SIGNED MULTIPLY
ROUTINE
; ARG1 * ARG2 ->
; PRODH:PRODL
; Test Sign Bit
; PRODH = PRODH
;
- ARG1
; Test Sign Bit
; PRODH = PRODH
;
- ARG2
TABLE 8-1: PERFORMANCE COMPARISON FOR VARIOUS MULTIPLY OPERATIONS
Routine
Multiply Method
Program
Memory
(Words)
Cycles
(Max)
Time
@ 40 MHz @ 10 MHz @ 4 MHz
Without hardware multiply
13
8 x 8 unsigned
Hardware multiply
1
Without hardware multiply
33
8 x 8 signed
Hardware multiply
6
Without hardware multiply
21
16 x 16 unsigned
Hardware multiply
28
Without hardware multiply
52
16 x 16 signed
Hardware multiply
35
69
6.9 µs
27.6 µs
69 µs
1
100 ns
400 ns
1 µs
91
9.1 µs
36.4 µs
91 µs
6
600 ns
2.4 µs
6 µs
242
24.2 µs
96.8 µs 242 µs
28
2.8 µs
11.2 µs
28 µs
254
25.4 µs 102.6 µs 254 µs
40
4.0 µs
16.0 µs
40 µs
2004 Microchip Technology Inc.
Preliminary
DS39631A-page 89
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