PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 61

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

6.0
6.1
An 8 x 8 hardware multiplier is included in the ALU of
the PIC18CXX2 devices. By making the multiply a
hardware operation, it completes in a single instruction
cycle. This is an unsigned multiply that gives a 16-bit
result. The result is stored into the 16-bit product regis-
ter pair (PRODH:PRODL). The multiplier does not
affect any flags in the ALUSTA register.
TABLE 6-1:
8 x 8 unsigned
8 x 8 signed
16 x 16 unsigned
16 x 16 signed
7/99 Microchip Technology Inc.
Routine
8 X 8 HARDWARE MULTIPLIER
Introduction
PERFORMANCE COMPARISON
Without hardware multiply
Hardware multiply
Without hardware multiply
Hardware multiply
Without hardware multiply
Hardware multiply
Without hardware multiply
Hardware multiply
Multiply Method
Preliminary
Program
Memory
(Words)
13
33
21
24
52
36
1
6
Making the 8 x 8 multiplier execute in a single cycle
gives the following advantages:
• Higher computational throughput
• Reduces code size requirements for multiply algo-
The performance increase allows the device to be used
in applications previously reserved for Digital Signal
Processors.
Table 6-1 shows a performance comparison between
enhanced devices using the single cycle hardware mul-
tiply, and performing the same function without the
hardware multiply.
rithms
Cycles
(Max)
242
254
69
91
24
36
1
6
@ 40 MHz
24.2 s
25.4 s
100 ns
600 ns
6.9 s
9.1 s
2.4 s
3.6 s
PIC18CXX2
@ 10 MHz
102.6 s
27.6 s
36.4 s
96.8 s
14.4 s
Time
400 ns
2.4 s
9.6 s
DS39026B-page 61
@ 4 MHz
242 s
254 s
69 s
91 s
24 s
36 s
1 s
6 s