ICM7217CIPL datasheet(13/19 Pages) RENESAS

13 / 19 page

ICM7217

FN3167 Rev 3.00

Page 13 of 19

July 2001

Applications

3-Level Inputs

ICM7217 has three inputs with 3-level logic states; High, Low

and Disconnected. These inputs are: LOAD REGISTER/OFF,

LOAD COUNTER/I/O OFF and DISPLAY CONT.

The circuits illustrated on Figure 11 can be used to drive these

inputs in different applications.

Fixed Decimal Point

In the common anode versions, a fixed decimal point may be acti-

vated by connecting the DP segment lead from the appropriate

digit (with separate digit displays) through a 39

 series resistor

to Ground. With common cathode devices, the DP segment

lead should be connected through a 75

 series resistor to

VDD.

To force the device to display leading zeroes after a fixed deci-

mal point, use a bipolar transistor and base resistor in a config-

uration like that shown in Figure 12 with the resistor connected

to the digit output driving the DP for left hand DP displays, and

to the next least significant digit output for right hand DP dis-

play.

Driving Larger Displays

For displays requiring more current than the ICM7217 can pro-

vide, the circuits of Figure 13 can be used.

LCD Display Interface

The low-power operation of the ICM7217 makes an LCD inter-

face desirable. The Intersil ICM7211 4-digit, BCD-to-LCD dis-

play driver easily interfaces to the ICM7217 as shown in Figure

14. Total system power consumption is less than 5mW. System

timing margins can be improved by using capacitance to ground

to slow down the BCD lines.

The 10k

 - 20k resistors on the switch BCD lines serve to

isolate the switches during BCD output.

Unit Counter with BCD Output

The simplest application of the ICM7217 is a 4-digit unit

counter (Figure 18). All that is required is an ICM7217, a power

supply and a 4 digit display. Add a momentary switch for reset,

an SPDT center-off switch to blank the display or view leading

zeroes, and one more SPDT switch for up/ down control. Using

an ICM7217A with a common-cathode calculator-type display

results in the least expensive digital counter/display system

available.

Inexpensive Frequency Counter/ Tachometer

This circuit uses the low power ICM7555 (CMOS 555) to gen-

erate the gating, STORE and RESET signals as shown in Fig-

ure 19. To provide the gating signal, the timer is con- figured as

an a stable multivibrator, using RA, RB and C to provide an

output that is positive for approximately one second and nega-

tive for approximately 300

s - 500s. The positive waveform

time is given by tWP = 0.693 (RA + RB)C while the negative

waveform is given by two = 0.693 RBC. The system is cali-

brated by using a 5M

 potentiometer for RA as a “coarse” con-

trol and a 1k

 potentiometer for RB as a “fine” control.

CD40106Bs are used as a monostable multivibrator and reset

time delay.

Tape Recorder Position Indicator/controller

The circuit in Figure 20 shows an application which uses the

up/down counting feature of the ICM7217 to keep track of tape

position. This circuit is representative of the many applications

of up/down counting in monitoring dimensional position.

In the tape recorder application, the LOAD REGISTER,

EQUAL and ZERO outputs are used to control the recorder. To

make the recorder stop at a particular point on the tape, the

used to stop the recorder either on fast forward, play or rewind.

To make the recorder stop before the tape comes free of the

reel on rewind, a leader should be used. Resetting the counter

at the starting point of the tape, a few feet from the end of the

leader, allows the ZERO output to be used to stop the recorder

on rewind, leaving the leader on the reel.

The 1M

 resistor and 0.0047F capacitor on the COUNT

INPUT provide a time constant of about 5ms to debounce the

reel switch. The Schmitt trigger on the COUNT INPUT of the

ICM7217 squares up the signal before applying it to the

counter. This technique may be used to debounce

switch-closure inputs in other applications.

Precision Elapsed Time/Countdown Timer

The circuit in Figure 21 uses an ICM7213 precision one

minute/one second timebase generator using a 4.1943MHz

crystal for generating pulses counted by an ICM7217B. The

thumbwheel switches allow a starting time to be entered into

the counter for a preset-countdown type timer, and allow the

a 24-hour clock with BCD output the register can be preset

with 2400 and the EQUAL output used to reset the counter.

Note the 10K resistor connected between the LOAD

COUNTER terminal and Ground. This resistor pulls the LOAD

COUNTER input low when not loading, thereby inhibiting the

BCD output drivers. This resistor should be eliminated and

SW4 replaced with an SPDT center-off switch if the BCD

outputs are to be used.

This technique may be used on any 3-level input. The 100k



pullup resistor on the count input is used to ensure proper logic

voltage swing from the ICM7213. For a less expensive (and

less accurate) timebase, an ICM7555 timer may be used in a

configuration like that shown in Figure 19 to generate a 1Hz

reference.

8-Digit Up/Down Counter

This circuit (Figure 22) shows how to cascade counters and

retain correct leading zero blanking. The NAND gate detects

whether a digit is active since one of the two segments a or b is

active on any unblanked number. The flip flop is clocked by the

least significant digit of the high order counter, and if this digit

is not blanked, the Q output of the flip flop goes high and turns

on the NPN transistor, thereby inhibiting leading zero blanking

on the low order counter.

It is possible to use separate thumbwheel switches for

presetting, but since the devices load data with the oscillator

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