ICM7216B, ICM7216D

FN3166 Rev.4.00

Page 13 of 18

Jan 7, 2004

Test Circuit

Typical Applications

The lCM7216 has been designed for use in a wide range of

Universal and Frequency counters. In many cases, prescalers will

be required to reduce the input frequencies to under 10MHz.

Because INPUT A and INPUT B are digital inputs, additional

circuitry is often required for input buffering, amplification,

hysteresis, and level shifting to obtain a good digital signal.

The lCM7216B can be used as a minimum component

complete Universal Counter as shown in Figure 15. This circuit

can use input frequencies up to 10MHz at INPUT A and 2MHz

at INPUT B. If the signal at INPUT A has a very low duty cycle

it may be necessary to use a 74LS121 monostable

multivibrator or similar circuit to stretch the input pulse width to

be able to guarantee that it is at least 50ns in duration.

To measure frequencies up to 40MHz the circuit of Figure 16

can be used. To obtain the correct measured value, it is

necessary to divide the oscillator frequency by four as well as

the input frequency. In doing this the time between

measurements is also lengthened to 800ms and the display

multiplex rate is decreased to 125Hz.

If the input frequency is prescaled by ten, then the oscillator

can remain at 10MHz or 1MHz, but the decimal point must be

moved one digit to the right. Figure 17 shows a frequency

no external decimal point control with the lCM7216B, the

decimal point may be controlled externally with additional

drivers as shown in Figure 17. Alternatively, if separate anodes

are available for the decimal points, they can be wired up to the

adjacent digit anodes. Note that there can be one zero to the

left of the decimal point since the internal leading zero blanking

cannot be changed. In Figure 18 additional logic has been

added to count the input directly in period mode for maximum

accuracy. In Figures 17 and 18, INPUT A comes from QC of

the prescaler rather than QD to obtain an input duty cycle of

40%.

FUNCTION

28

27

26

25

24

23

22

21

20

19

18

17

16

15

1

2

3

4

5

6

7

8

9

10

11

12

13

14

a

b

c

d

e

f

g

DP

INPUT A

100pF

INPUT B

10K

DP

D1

D2

D3

D4

D8

D5

F

P

FR

TI.

U.C.

O.F.

RESET

LED

OVERFLOW

INDICATOR

D8

D8

D7

D6

D5

D4

D3

D2

D1

D1

D2

D3

D4

.01/1

.1/10

1/100

10/1K

10k



D1

D2

D3

D4

D5

D6

D7

D8

ICM7216A

e

g

a

d

b

c

f

10k



10k



22M



10MHz

CRYSTAL

39pF

TYP

DISPLAY

BLANK

DISPLAY

TEST 1MHz

EXT

TEST

OSC

39pF

D4

D8

D2

D1

D5

EXT

OSC

INPUT

TYPICAL CRYSTAL SPECS:

F = 10MHz PARALLEL RESONANCE

FUNCTION

RANGE

8

8

4

6

8

HOLD

GENERATOR

FUNCTION

GENERATOR

1N914s

FIGURE 14. TEST CIRCUIT (ICM7216A SHOWN, OTHERS SIMILAR)