HCS361 datasheet(9/42 Pages) MICROCHIP

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DS40146F-page 9

HCS361

3.5.10

SEED: ENABLE SEED

TRANSMISSION

If SEED = 0, seed transmission is disabled. The Inde-

pendent Counter mode can only be used with seed

transmission disabled since SEED_2 is shared with the

second synchronization counter.

With SEED = 1, seed transmission is enabled. The

appropriate button code(s) must be activated to trans-

mit the seed information. In this mode, the seed infor-

mation (SEED_0, SEED_1, and SEED_2) and the

upper 12 or 16 bits of the serial number (SER_1)are

transmitted instead of the hop code.

Seed transmission is available for function codes

(Table 3-2) S[3:0] = 1001 and S[3:0] = 0011 (delayed).

This takes place regardless of the setting of the IND bit.

The two seed transmissions are shown in Figure 3-3.

FIGURE 3-3:

Seed Transmission

3.5.11

TMPSD: TEMPORARY SEED

TRANSMISSION

The temporary seed transmission can be used to dis-

able learning after the transmitter has been used for a

programmable number of operations. This feature can

be used to implement very secure systems. After learn-

ing is disabled, the seed information cannot be

accessed even if physical access to the transmitter is

possible. If TMPSD = 1 the seed transmission will be

disabled after a number of code hopping transmis-

sions. The number of transmissions before seed trans-

mission is disabled, can be programmed by setting the

synchronization counter (SYNC_A or SYNC_B) to a

value as shown in Table 3-4.

TABLE 3-4:

SYNCHRONOUS COUNTER

INITIALIZATION VALUES

All examples shown with XSER = 1, SEED = 1

When S[3:0] = 1001, delay is not applicable.

CRC+VLOW

SER_1

SEED_2

SEED_1

SEED_0

Data transmission direction

For S[3:0] = 0x3 before delay:

16-bit Data Word

16-bit Counter

Encrypt

CRC+VLOW

SER_1

SER_0

Encrypted Data

For S[3:0] = 0011 after delay (Note 1, Note 2):

CRC+VLOW

SER_1

SEED_2

SEED_1

SEED_0

Data transmission direction

Note 1: For Seed Transmission, SEED_2 is transmitted instead of SER_0.

2: For Seed Transmission, the setting of DELM has no effect.

Synchronous Counter

Values

Number of

Transmissions

0000H

128

0060H

0050H

0048H

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