PIC18F-LF1XK50 MICROCHIP [Microchip Technology], PIC18F-LF1XK50 Datasheet - Page 65

• Manufacturer Part Number: PIC18F-LF1XK50
• Description: 20-Pin USB Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

6.0
6.1
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
6.2
Example 6-1
unsigned multiplication. Only one instruction is required
when one of the arguments is already loaded in the
WREG register.
Example 6-2
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.
TABLE 6-1:
 2010 Microchip Technology Inc.
16 x 16 unsigned
8 x 8 unsigned
16 x 16 signed
8 x 8 signed
Routine
8 x 8 HARDWARE MULTIPLIER
Introduction
Operation
shows the instruction sequence for an 8 x 8
shows the sequence to do an 8 x 8 signed
PERFORMANCE COMPARISON FOR VARIOUS MULTIPLY OPERATIONS
Without hardware multiply
Without hardware multiply
Without hardware multiply
Without hardware multiply
Hardware multiply
Hardware multiply
Hardware multiply
Hardware multiply
Multiply Method
Table
6-1.
Preliminary
Program
Memory
(Words)
13
33
21
28
52
35
1
6
EXAMPLE 6-1:
EXAMPLE 6-2:
MOVF
MULWF
MOVF
MULWF
BTFSC
SUBWF
MOVF
BTFSC
SUBWF
Cycles
(Max)
242
254
69
91
28
40
1
6
ARG1, W
ARG2
ARG1, W
ARG2
ARG2, SB
PRODH, F
ARG2, W
ARG1, SB
PRODH, F
PIC18F/LF1XK50
@ 40 MHz
24.2 s
25.4 s
100 ns
600 ns
6.9 s
9.1 s
2.8 s
4.0 s
8 x 8 UNSIGNED
MULTIPLY ROUTINE
8 x 8 SIGNED MULTIPLY
ROUTINE
;
; ARG1 * ARG2 ->
; PRODH:PRODL
; ARG1 * ARG2 ->
; PRODH:PRODL
; Test Sign Bit
; PRODH = PRODH
;
; Test Sign Bit
; PRODH = PRODH
;
@ 10 MHz
102.6 s
27.6 s
36.4 s
96.8 s
16.0 s
11.2 s
Time
400 ns
2.4 s
- ARG1
- ARG2
DS41350E-page 65
@ 4 MHz
242 s
254 s
69 s
91 s
28 s
40 s
1 s
6 s