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LS7222 데이터시트(PDF) 2 Page - LSI Computer Systems |
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LS7222 데이터시트(HTML) 2 Page - LSI Computer Systems |
2 / 4 page Program Mode - The current Arm/Disarm/Duress codes may be altered to any value by initializing the Program mode. The steps involved for altering the codes are: 1. Enter the current Disarm code causing the Disarm output to go high. 2. Before the keypad entry enable time expires, enter the key corresponding to matrix position X4 Y1 two times. This will cause the Program Mode output to latch high, indicating that the circuit is now in the Program mode. The keypad entry enable timer is disabled during the Program mode. 3. Enter a 6-digit number from the keypad. The Program Mode output will latch low, indicating that the new codes have suc- cessfully been programmed. Of the 6 digits, the first 4 con- stitute the Arm code; the first 3 and the 5th constitute the Dis- arm code and the first 3 and the 6th constitute the Duress code. If an error is introduced or it is desired to change the codes before the 6th digit is typed, enter the key X4 Y3. This will reset the internal memory pointer of the LS7222 and a new 6-digit number can be entered. KEYPAD INTERFACE - The four X inputs and four Y outputs are designed for keypad interface (see Fig. 2). Since the X inputs have 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 than one LS7222 may share the same keypad. During normal operation the LS7222 will scan the matrix looking for a switch closure. Once a closure has been detected, the internal key debounce logic determines if a "valid" key has been pressed or that if noise is just present. Only one valid input will be generated with any key closure. The use of internal key debouncing and Schmitt triggers on the inputs provides the LS7222 with very high noise immunity. TAMPER - When a valid key has been detected by the LS7222, the entry is compared against the appropriate reference in the inter- nal memory. If the requirements of digit value and code sequential position are not fulfilled, the Tamper output will momentarily go high; this indicates that an illegal code entry was attempted. The keypad entry enable timer and memory pointer will both be reset so that entry of the code can be attempted again. TABLE 1. PIN DESCRIPTIONS PIN FUNCTION DESCRIPTION 1 Vss Supply voltage negative. 2 RC-OSC 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. 3, 4, 5, 6 X1, X2, X3, X4 The four X inputs and four Y outputs are designed to interface to a keypad matrix 7, 8, 9, 10 Y1, Y2, Y3, Y4 whose maximum allowable size is 4 by 4. 11 PROGRAM MODE 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. 12 CAP-M A capacitor connected between this input and Vss controls the duration of the Arm, Disarm and Tamper outputs. 13 TAMPER 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. 14 ARM 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. 15 ALARM 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. 16 DISARM 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. 17 LOCK 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. 18 LOCK STATUS 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. 19 CAP-K 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.) 20 VDD Supply voltage positive. 7222-012901-2 |
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