FIGURE 10.

PROGRAMMABLE FREQUENCY DIVIDER

17

10

11

12

13

14

15

16

18

WB0

WB1

WB2

WB3

WB4

WB5

WB6

WB7

1

2

4

A

B

TRIG

7

RESET

8

9

OUT

Vss

ƒo

+V

ƒi

+V

3

LS7212

ƒi

ƒo

Case 1, Mode = DO;

ƒo

Case 2, Mode = DD;

CASE 1. MODE = DO or DR; PRESCALE FACTOR, S = 1

In this setup a frequency division of the input clock, ƒi by a factor of 2 to 257, in increments of 1 can be

obtained according to the equation:

ƒo =

where W (weighting factor) = 0 to 255

ƒi

W + 2

The ƒo pulse width is non-symmetrical (non-50% duty -cycle)

CASE 2. MODE = DD; PRESCALE FACTOR, S = 1

In this setup a frequency division of the input clock, ƒi by a factor of 2 to 512, in increments of 2 can be

obtained according to the equation:

ƒo =

where W (weighting factor) = 0 to 255

ƒi

2(W + 1)

The ƒo pulse widths are symmetrical with 50% duty -cycle

EXAMPLES OF CASE 1 and CASE 2 FREQUENCY DIVISIONS WITH W = 2

CLOCK