DIGITAL LOCK FOR AUTOMOTIVE IGNITIONS

FEATURES:

• 5040 Four-Digit Combinations (for a 10 digit Keypad)

• Combinations are Hard-Wire Programmed

• Sense Input Enables Operation

• Save Memory Feature for Valet Parking

• Convenience Delay Controlled by External Capacitor

• Static or Momentary Lock Control Output

• Save Memory and Lock Status Outputs

• LS7220 (DIP), LS7220-S (SOIC) - See Figure 1

DESCRIPTION:

The LS7220 is a MOS digital lock circuit. When wired to a ten-digit

keypad, the circuit will recognize one four-digit combination out of a

possible 5040 combinations.

The LS7220 is configured with the features required for an Auto-

motive Ignition Anti-Theft Digital Lock (See Figure 5).

These

features include Sense input which enables the IC, Save Memory

for Valet Parking, Convenience Delay to maintain Unlock condition

for short term interruptions of the Sense input and Save Status and

Lock Status outputs which can be used for direct drive of LED

indicators.

OPERATING DESCRIPTION: (Refer to Figures 2, 3, 4 and 5.)

When the Sense input goes high, the LS7220 is enabled. The Lock

Status output turns on and Save Status and LOCK outputs remain

off. When the programmed four-digit combination is entered from

the keypad, in proper sequence, LOCK turns on and Lock Status

turns off. If the Sense input is interrupted for a period of time great-

er than the Convenience Delay, the operating sequence must start

over. If the Sense input is interrupted for a period of time less than

the Convenience Delay, the operation of the LS7220 is unaffected.

A momentary high at the Save input sets the Save Memory and

causes the LS7220 to save an Unlock condition (Sequential Mem-

ory is set) for any time duration interruption of the Sense input (i.e.,

valet parking). The Save Status output turns on when Save Mem-

ory is set. The Lock input is used to reset the Save Memory and re-

turn the LS7220 to normal operation.

NOTE: Using a 3 x 4 keypad, the F key can be connected to the

Lock input and the # key to the Save input. Lock Status and Save

Status outputs can be used to drive red and green LED indicators,

respectively.

INPUT/OUTPUT DESCRIPTION: (Refer to Figure 4)

SENSE INPUT (Pin 1)

A high at this input causes CONVENIENCE DELAY to transition

high and enables recognition of the SELECTED KEYS when they

are inputted in proper sequence. Control logic for LOCK, LOCK

STATUS and SAVE STATUS outputs is also enabled. A low at

this input keeps all outputs off and resets the Sequential Memory if

Save Memory is not set.

Supply voltage negative terminal.

Vss (Pin 14)

Supply voltage positive terminal.

1

2

3

4

5

6

7

14

13

12

11

8

9

10

PIN ASSIGNMENT - TOP VIEW

SENSE IN

UNSELECTED KEYS

(RESET)

SELECTED KEYS

(IN SEQUENCE)

LOCK IN

LOCK OUT

CONVENIENCE

DELAY

SAVE IN

SAVE STATUS OUT

LOCK STATUS OUT

FIGURE 1.

7220-012703-1

January 2003

UNSELECTED KEYS (RESET) INPUT (Pin 2)

A high at this input resets the Sequential Detector for the

SELECTED KEYS inputs. This input must be wired to all digit keys

which are not part of the Four-Digit Combination.

SELECTED KEYS INPUTS (Pins 3, 4, 5, 6)

When these inputs are brought high in correct sequence, (i.e.,I1, I2,

I3, I4) the Sequential Memory is set if SENSE input is high. LOCK

output turns on and LOCK STATUS output turns off when the

Sequential Memory is set.

LOCK INPUT (Pin 7)

A high at this input resets the Save Memory. The SAVE STATUS

output turns off when this occurs.

LOCK STATUS OUTPUT (Pin 8)

This output is the complement of LOCK output when the SENSE

input is high. See NOTE.

SAVE STATUS OUTPUT (Pin 10)

This output turns on when Save Memory is set and SENSE input is

high. See NOTE.

SAVE INPUT (Pin 11)

A high at this input sets the Save Memory. If Save Memory is set

and Sequential Memory is set, the Save Memory will prevent the

Sequential Memory from being reset as a result of a change at the

SENSE Input. (See SAVE STATUS OUTPUT.)

CONVENIENCE DELAY I/O (Pin 12)

An external capacitor placed on this pin will delay the effect of

changes at the SENSE Input from affecting the outputs and the

condition of the Sequential Detector and Sequential Memory.

(See Figure 2)

LOCK OUTPUT (Pin 13)

This output turns on when the Sequential Memory is set and

SENSE input is high. See NOTE.

NOTE: Outputs are off when SENSE input is low.

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

LS7220

UL

®

A3800