Single Chip 8 Digit Frequency Counters ICM7216
The ICM7216B is a fully integrated Timer Counters with LED display drivers. They combine a high frequency oscillator, a decade timebase counter, an 8-decade data counter and latches, a 7-segment decoder, digit multiplexers and 8-segment and 8-digit drivers which directly drive large multiplexed LED displays. The counter inputs have a maximum frequency of 10MHz in frequency and unit counter modes and 2MHz in the other modes. Both inputs are digital inputs. In many applications, amplification and level shifting will be required to obtain proper digital signals for these inputs.
The ICM7216B can function as a frequency counter, period counter, frequency ratio (fA/fB) counter, time interval counter or as a totalizing counter. The counter uses either a 10MHz or 1MHz quartz crystal timebase. For period and time interval, the 10MHz timebase gives a 0.1 μs resolution. In period average and time interval average, the resolution can be in the nanosecond range. In the frequency mode, the user can select accumulation times of 0.01s, 0.1s, 1s and 10s. With a 10s accumulation time, the frequency can be displayed to a resolution of 0.1Hz in the least significant digit. There is 0.2s between measurements in all ranges.
The ICM7216D functions as a frequency counter only, as described above.
All versions of the ICM7216 incorporate leading zero blanking. Frequency is displayed in kHz. In the ICM7216B, time is displayed in μs. The display is multiplexed at 500Hz with a 12.2% duty cycle for each digit. The ICM7216B and ICM7216D are designed for common cathode displays with typical peak segment currents of 12mA. In the display off mode, both digit and segment drivers are turned off, enabling the display to be used for other functions.
Feature Of Single Chip 8 Digit Frequency Counters ICM7216
- Functions as a frequency counter (DC to 10MHz)
- Four internal gate times: 0.01s, 0.1s, 1s, 10s in frequency counter mode
- Directly drives digits and segments of large multiplexed LED displays (common anode and common cathode versions)
- Single nominal 5V supply required
- Highly stable oscillator, uses 1MHz or 10MHz crystal
- Internally generated decimal points, interdigit blanking, leading zero blanking and overflow indication
- Display off mode turns off display and puts chip into low power mode
- Hold and reset inputs for additional flexibility
Pinout Of Single Chip 8 Digit Frequency Counters ICM7216
Block Diagram Of Single Chip 8 Digit Frequency Counters ICM7216
Pin Description Of Single Chip 8 Digit Frequency Counters ICM7216
INPUTS A and B
INPUTS A and B are digital inputs with a typical switching threshold of 2V at VDD = 5V. For optimum performance the peak-to-peak input signal should be at least 50% of the supply voltage and centered about the switching voltage. When these inputs are being driven from TTL logic, it is desirable to use a pullup resistor. The circuit counts high to low transitions at both inputs. (INPUT B is available only on lCM7216B).
Note that the amplitude of the input should not exceed the device supply (above the VDD and below the VSS) by more than 0.3V, otherwise the device may be damaged.
The FUNCTION, RANGE, CONTROL and EXTERNAL DECIMAL POINT inputs are time multiplexed to select the function desired. This is achieved by connecting the appropriate Digit driver output to the inputs. The function, range and control inputs must be stable during the last half of each digit output, (typically 125 μs). The multiplexed inputs are active low for the common cathode lCM7216B and lCM7216D.
Noise on the multiplex inputs can cause improper operation. This is particularly true when the unit counter mode of operation is selected, since changes in voltage on the digit drivers can be capacitively coupled through the LED diodes to the multiplex inputs. For maximum noise immunity, a 10kΩ resistor should be placed in series with the multiplexed inputs as shown in the application circuits.
The six functions that can be selected are: Frequency, Period, Time Interval, Unit Counter, Frequency Ratio and Oscillator Frequency. This input is available on the lCM7216B only.
The implementation of different functions is done by routing the different signals to two counters, called “Main Counter” and “Reference Counter”. A simplified block diagram of the device for functions realization is shown in the following picture.
The output of the Main Counter is the information which goes to the display. The Reference Counter divides its input by 1, 10, 100 and 1000. One of these outputs will be selected through the range selector and drive the enable input of the Main Counter. This means that the Reference Counter, along with its associated blocks, directs the Main Counter to begin counting and determines the length of the counting period. Note that picture above does not show the complete functional diagram (See the Functional Block Diagram). After the end of each counting period, the output of the Main Counter will be latched and displayed, then the counter will be reset and a new measurement cycle will begin. Any change in the FUNCTION INPUT will stop the present measurement without updating the display and then initiate a new measurement. This prevents an erroneous first reading after the FUNCTION INPUT is changed. In all cases, the 1-0 transitions are counted or timed.
- 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 0.0001 μs 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 frequency at input A should be higher than input B for meaningful result. The result in this case is unitless and its resolution can go up to three 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 transition 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 completion. 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.
The RANGE INPUT selects whether the measurement period is made for 1, 10, 100 or 1000 counts of the Reference Counter. 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 measurement. This prevents an erroneous first reading after the RANGE INPUT is changed.
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 the picture below). 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 this input and the VDD or VSS.
- Display Off – To disable the display drivers, it is necessary to tie the D4 line to the CONTROL INPUT and have the HOLD input at VDD. While in Display Off mode, the segments and digit drivers are all off, leaving the display lines floating, so the display can be shared with other devices. In this mode, the oscillator continues to run with a typical supply current of 1.5mA with a 10MHz crystal, but no measurements are made and multiplexed inputs are inactive. A new measurement cycle will be initiated when the HOLD input is switched to VSS.
- Display Test – Display will turn on with all the digits showing 8s and all decimal points on. The display will be blanked if Display Off is selected at the same time.
- 1MHz Select – The 1MHz select mode allows use of a 1MHz crystal with the same digit multiplex rate and time between measurement as with a 10MHz crystal. This is done by dividing the oscillator frequency by 104 rather than 105. The decimal point is also shifted one digit to the right in period and time interval, since the least significant digit will be in μs increment rather than 0.1 μs increment.
- External Oscillator Enable – In this mode, the signal at EXT OSC INPUT is used as a timebase instead of the on-board crystal oscillator (built around the OSC INPUT, OSC OUTPUT inputs). This input can be used for an external stable temperature compensated crystal oscillator or for special measurements with any external source. The on-board crystal oscillator continues to work when the external oscillator is selected. This is necessary to avoid hang-up problems, and has no effect on the chip’s functional operation. If the on-board oscillator frequency is less than 1MHz or only the external oscillator is used, the OSC INPUT must be connected to the EXT OSC INPUT providing the timebase has enough voltage swing for OSC INPUT (See Electrical Specifications). If the external timebase is TTL level a pullup resistor must be used for OSC INPUT. The other way is to put a 22MΩ resistor between OSC INPUT and OSC OUTPUT and capacitively couple the EXT OSC INPUT to OSC INPUT. This will bias the OSC INPUT at its threshold and the drive voltage will need to be only 2VP-P. The external timebase frequency must be greater than 100kHz or the chip will reset itself to enable the on-board oscillator.
- External Decimal Point Enable – In this mode, the EX DP INPUT is enabled (lCM7216D only). A decimal point will be displayed for the digit that its output line is connected to this 10 input (EX DP INPUT). Digit 8 should not be used since it will override the overflow output. Leading zero blanking is effective for the digits to the left of selected decimal point.
Except in the unit counter mode, when the HOLD input is at VDD, any measurement in progress (before STORE goes low) is stopped, the main counter is reset and the chip is held ready to initiate a new measurement as soon as HOLD goes low. The latches which hold the main counter data are not updated, so the last complete measurement is displayed. In unit counter mode when HOLD input is at VDD, the counter is not stopped or reset, but the display is frozen at that instantaneous value. When HOLD goes low the count continues from the new value in the new counter.
The RESET input resets the main counter, stops any measurement in progress, and enables the main counter latches, resulting in an all zero output. A capacitor to ground will prevent any hang-ups on power-up.
Measurement In Progress
This output is provided in lCM7216D. It stays low during measurements and goes high for intervals between measurements. It is provided for system interfacing and can drive a low power Schottky TTL or one ECL load if the ECL device is powered from the same supply as lCM7216D.
Decimal Point Position
The decimal point position for different modes of lCM7216 operation. Note that the digit 1 is the least significant digit for 10MHz timebase frequency.
When overflow happens in any measurement it will be indicated on the decimal point of the digit 8. A separate LED indicator can be used. The following picture shows how to connect this indicator.