9-18

Frequency - In this mode input A is counted by the Main

Counter for a precise period of time. This time is determined

by the time base oscillator and the selected range. For the

10MHz (or 1MHz) time base, the resolutions are 100Hz,

10Hz, 1Hz and 0.1Hz. The decimal point on the display is

set for kHz reading.

Period - In this mode, the timebase oscillator is counted by

the Main Counter for the duration of 1, 10, 100 or 1000

(range selected) periods of the signal at input A. A 10MHz

timebase gives resolutions of 0.1

µs to 0.0001µs for 1000

periods averaging. Note that the maximum input frequency

for period measurement is 2.5MHz.

Frequency Ratio - In this mode, the input A is counted by

the Main Counter for the duration of 1, 10, 100 or 1000

(range selected) periods of the signal at input B. The fre-

quency at input A should be higher than input B for meaning-

ful result. The result in this case is unitless and its resolution

can go up to 3 digits after decimal point.

Time Interval - In this mode, the timebase oscillator is

counted by the Main Counter for the duration of a 1-0 transi-

tion of input A until a 1-0 transition of input B. This means

input A starts the counting and input B stops it. If other ranges,

except 0.01s/1 cycle are selected the sequence of input A and

B transitions must happen 10, 100 or 1000 times until the

display becomes updated; note this when measuring long

time intervals to give enough time for measurement comple-

tion. The resolution in this mode is the same as for period

measurement. See the Time Interval Measurement section

also.

Unit Counter - In this mode, the Main Counter is always

enabled. The input A is counted by the Main Counter and

displayed continuously.

Oscillator Frequency - In this mode, the device makes a

frequency measurement on its timebase. This is a self test

mode for device functionality check. For 10MHz timebase

the display will show 10000.0, 10000.00, 10000.000 and

Overflow in different ranges.

Range Input

The RANGE INPUT selects whether the measurement

period is made for 1, 10, 100 or 1000 counts of the Refer-

ence Counter. As it is shown in Table 1, this gives different

counting windows for frequency measurement and various

cycles for other modes of measurement.

In all functional modes except Unit Counter, any change in

the RANGE INPUT will stop the present measurement

without updating the display and then initiate a new mea-

surement. This prevents an erroneous first reading after the

RANGE INPUT is changed.

Control Input

Unlike the other multiplexed inputs, to which only one of the

digit outputs can be connected at a time, this input can be

tied to different digit lines to select combination of controls.

In this case, isolation diodes must be used in digit lines to

avoid crosstalk between them (see Figure 17). The direction

of diodes depends on the device version, common anode or

common cathode. For maximum noise immunity at this input,

in addition to the 10K resistor which was mentioned before,

a 39pF to 100pF capacitor should also be placed between

Display Off - To disable the display drivers, it is necessary to

tie the D4 line to the CONTROL INPUT and have the HOLD

INTERNAL CONTROL

100Hz

INPUT A

INPUT B

INPUT

SELECTOR

INTERNAL OR

EXTERNAL

OSCILLATOR

INPUT A

ENABLE

CLOCK

MAIN COUNTER

RANGE SELECTOR

÷1

÷10

÷100 ÷1000

INTERNAL CONTROL

INTERNAL CONTROL

CLOCK

INTERNAL CONTROL

INPUT

SELECTOR

REFERENCE COUNTER

FIGURE 11. SIMPLIFIED BLOCK DIAGRAM OF FUNCTIONS IMPLEMENTATION

TABLE 2. 7216A/B INPUT ROUTING

FUNCTION

MAIN

COUNTER

REFERENCE COUNTER

Input A

100Hz (Oscillator

Oscillator

Input A

Input A

Input B

Time Interval

(A

→B)

Oscillator

Input A

Input B

Unit Counter

(Count A)

Input A

Not Applicable

Osc. Freq.

Oscillator

100Hz (Oscillator

ICM7216A, ICM7216B, ICM7216D