Datasheet ICM7216A (Intersil) - 8

ICM7216A, ICM7216B, ICM7216D Description COUNTED TRANSITIONS INPUTS A and B
INPUTS A and B are digital inputs with a typical switching
50ns MIN
threshold of 2.0V at VDD = 5.0V. For optimum performance
4.5V INPUT A
the peak-to-peak input signal should be at least 50% of the
0.5V
supply voltage and centered about the switching voltage.
50ns MIN tR = tF = 10ns
When these inputs are being driven from TTL logic, it is desirable to use a pullup resistor. The circuit counts high to
FIGURE 9. WAVEFORM FOR GUARANTEED MINIMUM fA(MAX)
low transitions at both inputs. (INPUT B is available only on
FUNCTION = FREQUENCY, FREQUENCY RATIO, UNIT COUNTER
lCM7216A and 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.
MEASURED INTERVAL Multiplexed Inputs 250ns
The FUNCTION, RANGE, CONTROL and EXTERNAL
MIN
DECIMAL POINT inputs are time multiplexed to select the
INPUT A OR 4.5V
function desired. This is achieved by connecting the appro-
INPUT B 0.5V
priate Digit driver output to the inputs. The function, range
250ns tR = tF = 10s MIN
and control inputs must be stable during the last half of each digit output, (typically 125µs). The multiplexed inputs are active high for the common anode lCM7216A and active low
FIGURE 10. WAVEFORM FOR GUARANTEED MINIMUM fB(MAX)
for the common cathode lCM7216B and lCM7216D.
AND fA(MAX) FOR FUNCTION = PERIOD AND TIME INTERVAL
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
Function Input
drivers can be capacitively coupled through the LED diodes The six functions that can be selected are:
Frequency,
to the multiplex inputs. For maximum noise immunity, a 10kΩ
Period, Time Interval, Unit Counter, Frequency Ratio
and resistor should be placed in series with the multiplexed
Oscillator Frequency.
This input is available on the inputs as shown in the application circuits. lCM7216A and lCM7216B only. Table 1 shows the functions selected by each digit for these The implementation of different functions is done by routing inputs. the different signals to two counters, called “Main Counter”
TABLE 1. MULTIPLEXED INPUT FUNCTIONS
and “Reference Counter”. A simplified block diagram of the device for functions realization is shown in Figure 11. Table 2
FUNCTION DIGIT
shows which signals will be routed to each counter in FUNCTION INPUT (Pin Frequency D1 different cases. The output of the Main Counter is the 3, lCM7216A and B Period D8 information which goes to the display. The Reference Only) Frequency Ratio D2 Counter divides its input by 1, 10, 100 and 1000. One of these outputs will be selected through the range selector Time Interval D5 and drive the enable input of the Main Counter. This means Unit Counter D4 that the Reference Counter, along with its' associated Oscillator Frequency D3 blocks, directs the Main Counter to begin counting and RANGE INPUT, Pin 14 0.01s/1 Cycle D1 determines the length of the counting period. Note that Figure 11 does not show the complete functional diagram 0.1s/10 Cycles D2 (See the Functional Block Diagram). After the end of each 1s/100 Cycles D3 counting period, the output of the Main Counter will be 10s/1K Cycles D4 latched and displayed, then the counter will be reset and a CONTROL INPUT, Display Off D4 and new measurement cycle will begin. Any change in the Pin 1 Hold FUNCTION INPUT will stop the present measurement without updating the display and then initiate a new Display Test D8 measurement. This prevents an erroneous first reading after 1MHz Select D2 the FUNCTION INPUT is changed. In all cases, the 1-0 External Oscillator Enable D1 transitions are counted or timed. External Decimal Point D3 Enable External DP INPUT (Pin Decimal point is output for same digit 13, ICM7216D Only) that is connected to this input. 13-29