ICM7249 Datasheet, PDF (7/9 Pages) Intersil Corporation – 51/2 Digit LCD, Micro-Power Event/Hour Meter

ICM7249
TABLE 1. MODE SELECT TABLE
CONTROL PIN INPUTS
MODE C3 C2 C1 C0
FUNCTION
0
0 0 0 0 1 Hour Interval Timer
1
0 0 0 1 0.1 Hour Interval Timer
2
0 0 1 0 0.01 Hour Interval Timer
3
0 0 1 1 0.1 Minute Interval Timer
4
0 1 0 0 1’s Counter with Debounce
5
0 1 0 1 1’s Counter
6
0 1 1 0 10’s Counter with Debounce
7
0 1 1 1 10’s Counter
8
1 0 0 0 100’s Counter with Debounce
9
1 0 0 1 100’s Counter
10
1 0 1 0 1000’s Counter with Debounce
11
1 0 1 1 1000’s counter
12
1 1 0 0 Test Display Digits
13
1 1 0 1 Internal Test
14
1 1 1 0 Internal Test
15
1 1 1 1 Reset
Detailed Description
As the Functional Diagram shows the device consists of the
following building blocks:
• A 32.768kHz crystal oscillator with the associated dividers
to generate timebase signals for periods of 1s (frequency
of 1Hz), 6s (1/10 min) and 36s (1/100 hour), and 32Hz
signal for LCD drivers.
• A debounce/high-pass detect circuit for the S/S (Start/Stop)
input.
• A chain of cascaded decade counters, 3 decade counters
for prescaling and 5¹/₂ BCD decade counters for display
driving.
• Display control circuitry and BCD to 7-segment decoder/
drivers.
• A control decoder to select different modes of operation.
This is done by routing different signals to the different
points in the chain of decade counters.
The control decoder has 4 inputs for selecting 16 possible
modes of operation, numbered 0 to 15. The 16 modes are
selected by placing the binary equivalent of the mode num-
ber on inputs C0 to C3. Table 2 shows the control inputs and
the modes of operation.
After applying power, the ICM7249 requires a rise time of t_r
to become active and for oscillation to begin, as shown in
Figure 1. The BP (backplane) output changes state once
every 512 cycles of the crystal oscillator, resulting in a
square wave of 32Hz. The display segments drive signal has
the same level and frequency as BP. Segments are off when
in phase with BP and are on when out of phase with BP.
A non-multiplexed LCD display is used because it is more
stable over temperature and allows many standard LCD
displays to be used.
Timer Mode of Operation
In modes 0 to 3 the device functions as an interval timer. In
this mode, one of the timebase signals will be routed to the
decade counters at a proper point in the chain. Depending
on the selected mode the display will be incremented at 0.1
min, 0.01 hour, 0.1 hour or 1 hour rates.
Control of timing function is handled by the S/S input. There
is a high-pass filtering effect on the S/S input in timer modes.
Referring to Figure 2, timing is active when either S/S is held
high for more than 12.5ms, or if input frequency is 50Hz to
120kHz. Driving S/S with a frequency between 40Hz to 50Hz
has an indeterminate effect on timing and should be
avoided. Note that the t_HP intervals shown on Figure 1 are
also applied to the intervals when the S/S input is low.
Counter Mode of Operation
In modes 4 to 11 the device functions as an event counter or
totalizer. In this mode the S/S input will be routed to the decade
counters at a proper point in the chain. Each positive transition
of the S/S will be registered as one count. Depending on the
selected mode, the display will be incremented by each pulse,
every 10 pulses, every 100 pulses or every 1000 pulses.
In counter modes 4, 6, 8 and 10 the S/S input is subjected to
debounce filtering. Referring to Figure 4, only the pulses with
a frequency of less than 40Hz are valid and will be counted.
Input pulses with a frequency of 50Hz to 120kHz are not
counted individually, but each burst of input pulses will be
counted as one pulse if it lasts at least 12.5ms. Driving S/S
with a frequency between 40Hz to 50Hz has an indetermi-
nate result and should be avoided.
In counter modes 5, 7, 9 and 11 the S/S input is not
subjected to any debouncing action and input pulses will be
counted up to a frequency of 120kHz.
Wink Segment
The wink segment is provided as a annunciator to indicate the
ICM7249 is working. It can be connected to any kind of annun-
ciator on an LCD, like the flashing colons in a clock type LCD.
In the timer modes, the wink segment flashes while timing is
taking place. The wink segment waveform is shown on
Figure 3 for timer modes. On the positive transition of S/S,
the wink output turns off. It remains off for 16 BP cycles and
turns back on for another 16 cycles. If timing is still active,
this will be repeated, giving a wink flash rate of 1Hz; other-
wise, the wink segment remains on while timing is not active.
In the counter modes, the wink segment stays on until a
pulse occurs on S/S input, then it winks off indicating a pulse
is counted. This will happen regardless of whether the
display is incremented. Figure 5 shows the wink waveform
for counter modes. When a count occurs, the wink segment
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