ICM7226 Intersil Corporation, ICM7226 Datasheet - Page 11

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

Overflow Indication
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. Figure 14 shows how to connect this indicator.
LED overflow indicator connections: Overflow will be
indicated on the decimal point output of digit 8.
Time Interval Measurement
When in the time interval mode and measuring a single
event, the lCM7226A and lCM7226B must first be “primed”
prior to measuring the event of interest. This is done by first
generating a negative going edge on Channel A followed by a
negative going edge on Channel B to start the “measurement
interval”. The inputs are then primed ready for the measure-
ment. Positive going edges on A and B, before or after the
priming, will be needed to restore the original condition.
Priming can be easily accomplished using the circuit in
Figure 15.
Following the priming procedure (when in single event or 1
cycle range) the device is ready to measure one (only) event.
N.O.
FIGURE 15. PRIMING CIRCUIT, SIGNALS A AND B BOTH HIGH
ICM7226A
ICM7226B
FIGURE 14. SEGMENT IDENTIFICATION AND DISPLAY FONT
V
V
DD
SS
DEVICE
100K
PRIME
DEVICE
1
OR LOW
1
2
1N914
V
V
SIGNAL A
SIGNAL B
SS
DD
CD4049B Inverting Buffer
CD4070B Exclusive - OR
150K
0.1 F
e
Decimal Point
f
CATHODE
1
d
g
a
D8
c
b
TYPE
1
DP
10K
2
2
Decimal Point
V
ICM7226A, ICM7226B
ANODE
SS
D8
10nF
INPUT A
INPUT B
1
9-25
When timing repetitive signals, it is not necessary to “prime”
the lCM7226A and lCM7226B as the first alternating signal
states automatically prime the device. See Figure 1.
During any time interval measurement cycle, the ICM7226A
and lCM7226B requires 200ms following B going low to
update all internal logic. A new measurement cycle will not
take place until completion of this internal update time.
Oscillator Considerations
The oscillator is a high gain complementary FET inverter. An
external resistor of 10M
between the oscillator input and output to provide biasing.
The oscillator is designed to work with a parallel resonant
10MHz quartz crystal with a static capacitance of 22pF and
a series resistance of less than 35 . Among suitable
crystals is the 10MHz CTS KNIGHTS ISI-002.
For a specific crystal and load capacitance, the required g
can be calculated as follows:
C
R
C
C
The required g
for the lCM7226 to insure reliable startup. The OSCillator
INPUT and OUTPUT pins each contribute about 4pF to C
and C
C
static capacitance.
In cases where non decade prescalers are used, it may be
desirable to use a crystal which is neither 10MHz or 1MHz.
In that case both the multiplex rate and time between
measurements will be different. The multiplex rate is:
1MHz mode. The time between measurements is
the 10MHz mode and
The buffered oscillator output should be used as an oscillator
test point or to drive additional logic; this output will drive one
low power Schottky TTL load. When the buffered oscillator
output is used to drive CMOS or the external oscillator input,
a 10k
output to V
The crystal and oscillator components should be located as
close to the chip as practical to minimize pickup from other
signals. Coupling from the EXTERNAL OSClLLATOR INPUT
to the OSClLLATOR OUTPUT or INPUT can cause
undesirable shifts in oscillator frequency.
g
where C
f
MUX
M
O
S
IN
OUT
OUT
= 2 f
= Crystal Series Resistance
=
= Crystal Static Capacitance
= Input Capacitance
=
= Output Capacitance
OUT
should be approximately twice the specified crystal
2
L
resistor should be added from the buffered oscillator
------------------ -
2 10
C
f
=
OSC
IN
DD
. For maximum stability of frequency, C
-------------------------------- -
C
C
C
4
.
IN
OUT
M
IN
for 10MHz mode and
+
should not exceed 50% of the g
C
C
OUT
R
OUT
S
2 10
------------------ -
1
f
OSC
+
C
------- -
C
or 22M
O
5
L
in the 1MHz mode.
2
f
should be connected
MUX
=
------------------ -
2 10
f
OSC
M
2 10
------------------ -
specified
3
f
OSC
IN
for the
6
and
IN
in
M