ICM7226 Intersil Corporation, ICM7226 Datasheet - Page 14

• Manufacturer Part Number: ICM7226
• Description: 8-Digit Multi-Function Frequency Counter/Timer
• Manufacturer: Intersil Corporation

Typical Applications
The ICM7226 has been designed as a complete stand alone
Universal Counter, or used with prescalers and other circuitry
in a variety of applications. Since INPUT A and INPUT B are
digital inputs, additional circuitry will be required in many
applications, for input buffering, amplification, hysteresis, and
level shifting to obtain the required digital voltages. For many
applications a FET source follower can be used for input buff-
ering, and an ECL 10116 line receiver can be used for amplifi-
cation and hysteresis to obtain high impedance input,
sensitivity and bandwidth. However, cost and complexity of
this circuitry can vary widely, depending upon the sensitivity
and bandwidth required. When TTL prescalers or input buffers
are used, a pull up resistors to V
optimal voltage swing at INPUTS A and B. If prescalers aren’t
required, the ICM7226 can be used to implement a minimum
component Universal Counter as shown in Figure 20.
6
RESET
D2
D5
D8
D4
A IN
B IN
0.1 F
D1
D3
D5
D6
D7
D8
10k
D3
D2
D4
8
39pF
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
D8
V
DD
DD
ICM7226B
should be used to obtain
D7
10k
FIGURE 20. 10MHz UNIVERSAL COUNTER
D6
ICM7226A, ICM7226B
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
DP
V
D5
g
e
a
b
c
f
DD
d
V+
V+
EXT OSC IN
100k
V
100k
9-28
DD
For input frequencies up to 40MHz, the circuit shown in
Figure 21 can be used to implement a frequency and
period counter. To obtain the correct value when measuring
frequency and period, it is necessary to divide the 10MHz
oscillator frequency down to 2.5MHz. In doing this the time
between measurements is lengthened to 800ms and the dis-
play multiplex rate is decreased to 125Hz.
If the input frequency is prescaled by ten, the oscillator
frequency can remain at either 10MHz or 1MHz, but the
decimal point must be moved. Figure 22 shows use of a 10
prescaler in frequency counter mode. Additional logic has
been added to enable the ICM7226 to count the input
directly in period mode for maximum accuracy.
D4
HOLD
39pF
V+
D3
D4
D1
D3
22M
D2
DISPLAY
BLANK
V+
D2
10MHz
CRYSTAL
39pF (TYP)
D4
1N914s
DISPLAY
TEST
8
4
D1
D8
DP
EXT OSC
ENABLE
a
b
c
d
e
g
f
D1
D8
3
TYPICAL
CRYSTAL
PARAMETERS
C
R
L
S
22pF
35