ICM7216A Intersil Corporation, ICM7216A Datasheet - Page 8

• Manufacturer Part Number: ICM7216A
• Description: 8-digit, Multi-function, Frequency Counters/timers
• Manufacturer: Intersil Corporation

Description
INPUTS A and B
INPUTS A and B are digital inputs with a typical switching
threshold of 2V at V
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
lCM7216A and lCM7216B).
Note that the amplitude of the input should not exceed the
device supply (above the V
than 0.3V, otherwise the device may be damaged.
Multiplexed Inputs
The FUNCTION, RANGE, CONTROL and EXTERNAL
DECIMAL POINT inputs are time multiplexed to select the
function desired. This is achieved by connecting the appro-
priate 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 s). The multiplexed inputs are
active high for the common anode lCM7216A and 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 10k
resistor should be placed in series with the multiplexed
inputs as shown in the application circuits.
Table 1 shows the functions selected by each digit for these
inputs.
FUNCTION INPUT (Pin
3, lCM7216A and B
Only)
RANGE INPUT, Pin 14
CONTROL INPUT,
Pin 1
External DP INPUT (Pin
13, ICM7216D Only)
TABLE 1. MULTIPLEXED INPUT FUNCTIONS
DD
= 5V. For optimum performance the
Frequency
Period
Frequency Ratio
Time Interval
Unit Counter
Oscillator Frequency
0.01s/1 Cycle
0.1s/10 Cycles
1s/100 Cycles
10s/1K Cycles
Display Off
Display Test
1MHz Select
External Oscillator Enable
External Decimal Point
Enable
Decimal point is output for same digit
that is connected to this input.
DD
and below the V
FUNCTION
ICM7216A, ICM7216B, ICM7216D
SS
) by more
D4 and
DIGIT
Hold
D1
D8
D2
D5
D4
D3
D1
D2
D3
D4
D8
D2
D1
D3
9-17
9.
Function Input
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
lCM7216A and 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 Figure 11. Table 2
shows which signals will be routed to each counter in
different cases. 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 Figure 11 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.
INPUT A OR
FIGURE 10. WAVEFORM FOR GUARANTEED MINIMUM f
INPUT A
FIGURE 9. WAVEFORM FOR GUARANTEED MINIMUM f
INPUT B
4.5V
0.5V
4.5V
0.5V
FUNCTION = FREQUENCY, FREQUENCY RATIO,
UNIT COUNTER
AND f
TIME INTERVAL
A
(MAX) FOR FUNCTION = PERIOD AND
50ns MIN
250ns
MIN
MEASURED
INTERVAL
250ns
MIN
t r = t f = 10ns
50ns MIN
COUNTED
TRANSITIONS
t r = t f = 10s
A
B
(MAX)
(MAX)