LS7222 View Datasheet(PDF) - LSI Corporation
Part Name
Description
Manufacturer
LS7222 Datasheet PDF : 4 Pages
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Program Mode - The current Arm/Disarm/Duress codes may be KEYPAD INTERFACE - The four X inputs and four Y outputs are
altered to any value by initializing the Program mode. The steps designed for keypad interface (see Fig. 2). Since the X inputs have
involved for altering the codes are:
internal pull-ups, the maximum matrix size of 4 x 4 does not have
to be utilized. Because the Y outputs have open drains, more
1. Enter the current Disarm code causing the Disarm output to than one LS7222 may share the same keypad.
go high.
During normal operation the LS7222 will scan the matrix looking for
2. Before the keypad entry enable time expires, enter the key a switch closure. Once a closure has been detected, the internal
corresponding to matrix position X4 Y1 two times. This will key debounce logic determines if a "valid" key has been pressed or
cause the Program Mode output to latch high, indicating that that if noise is just present. Only one valid input will be generated
the circuit is now in the Program mode. The keypad entry with any key closure. The use of internal key debouncing and
enable timer is disabled during the Program mode.
Schmitt triggers on the inputs provides the LS7222 with very high
noise immunity.
3. Enter a 6-digit number from the keypad. The Program Mode
output will latch low, indicating that the new codes have suc- TAMPER - When a valid key has been detected by the LS7222,
cessfully been programmed. Of the 6 digits, the first 4 con- the entry is compared against the appropriate reference in the inter-
stitute the Arm code; the first 3 and the 5th constitute the Dis- nal memory. If the requirements of digit value and code sequential
arm code and the first 3 and the 6th constitute the Duress position are not fulfilled, the Tamper output will momentarily go
code. If an error is introduced or it is desired to change the high; this indicates that an illegal code entry was attempted. The
codes before the 6th digit is typed, enter the key X4 Y3. This keypad entry enable timer and memory pointer will both be reset so
will reset the internal memory pointer of the LS7222 and a that entry of the code can be attempted again.
new 6-digit number can be entered.
PIN
1
2
3, 4, 5, 6
7, 8, 9, 10
11
12
13
14
15
16
17
18
19
20
7222-012901-2
FUNCTION
Vss
RC-OSC
X1, X2, X3, X4
Y1, Y2, Y3, Y4
PROGRAM MODE
CAP-M
TAMPER
ARM
ALARM
DISARM
LOCK
LOCK STATUS
CAP-K
VDD
TABLE 1. PIN DESCRIPTIONS
DESCRIPTION
Supply voltage negative.
Determines the LS7222's internal clock frequency, which is used for keyboard scanning
and debounce. A resistor (to VDD) and a capacitor (to Vss) connected to this input sets
the frequency.
The four X inputs and four Y outputs are designed to interface to a keypad matrix
whose maximum allowable size is 4 by 4.
This output goes high when the program mode is initiated. It resets to a low state after the
6-digit Arm/Disarm/Duress combination code has been programmed.
A capacitor connected between this input and Vss controls the duration of the Arm,
Disarm and Tamper outputs.
Whenever a key is entered that is not a valid code element, this output goes high for a
period determined by the capacitor on the CAP-M input.
This output generates an active high output every time the Arm code is entered,
irrespective of whether the circuit is currently in the disarm state or not. The duration of
this output is determined by the capacitor on the CAP-M input. When the Arm and Disarm
codes are identical , this output will occur on every other code entry.
When the Duress code is entered, this output latches high to enable an external alarm.
The Alarm output resets to a low state when the Arm code is entered again.
This output generates an active high output every time the Disarm code is entered,
irrespective of whether the circuit is currently in the armed state or not. The duration of
this output is determined by the capacitor on the CAP-M input. When the Arm and Disarm
codes are identical , this output will occur on every other code entry.
When the Disarm code or the Duress code is entered, this output latches high. When the
Arm code is entered, the output latches low. If the Disarm or Duress code is entered
when the output is already high (i.e. already disarmed), the output remains unaffected.
Similarly, if the Arm code is entered when the output is already low (i.e. already armed), it
remains unchanged. An exception to this rule is when the Arm and Disarm code identical
in all 4 digits. In that situation, the output will toggle every time the code is entered.
Functionally, this output is identical to the LOCK output, with the exception that its polarity
is reversed with respect to the LOCK output. This output is intended for driving a display
lamp to indicate the lock status.
A capacitor connected between this input and Vss sets the time limit for entering a 4 digit
code from the keypad. (6 digits when initiating the program mode.)
Supply voltage positive.
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