PIC18LC658-I/CL View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC18LC658-I/CL

High-Performance Microcontrollers with CAN Module

Microchip Technology 

PIC18CXX8

6.0 8 X 8 HARDWARE MULTIPLIER

An 8 x 8 hardware multiplier is included in the ALU of

the PIC18CXX8 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 STATUS register.

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-

rithms

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.

TABLE 6-1: PERFORMANCE COMPARISON

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 µs

27.6 µs

69 µs

Hardware multiply

1

1

100 ns

400 ns

1 µs

8 x 8 signed

Without hardware multiply

33

91

9.1 µs

36.4 µs

91 µs

Hardware multiply

6

6

600 ns

2.4 µs

6 µs

16 x 16 unsigned Without hardware multiply

21

242

24.2 µs

96.8 µs 242 µs

Hardware multiply

24

24

2.4 µs

9.6 µs

24 µs

16 x 16 signed Without hardware multiply

52

254

25.4 µs 102.6 µs 254 µs

Hardware multiply

36

36

3.6 µs

14.4 µs

36 µs

 2000 Microchip Technology Inc.

Advanced Information

DS30475A-page 71

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