HCS410

DS40158C-page 20

Preliminary

© 1997 Microchip Technology Inc.

3.4

60/64-bit Seed Word/Transport Code

This is the 60-bit seed code that is transmitted when

seed transmission is selected. This allows the system

designer to implement the secure learn feature or use

this fixed code word as part of a different key genera-

tion/tracking process or purely as a fixed code trans-

mission. The seed is not available in IFF2-mode. A

Seed transmission can be initiated in two ways,

depending on the button inputs (Figure 3-1)

Seed transmission is available for function codes

(Table 2-2) S[2:0] = 111 and S[2:0] = 011 (delayed).

The delayed seed transmission starts with a normal

code hopping transmission being transmitted for 3 sec-

onds, before switching to a seed transmission. The two

seed transmissions are shown in Figure 3-1.

The least significant 32-bits of the seed are used as the

transport code. The transport code is used to write-pro-

tect the serial number, configuration word, as well as

preventing accidental programming of the HCS410

when in IFF mode.

3.5

Encoder Serial Number

There are 32 bits allocated for the serial number and a

selectable

configuration

bit

(XSER)

determines

whether 32 or 28 bits will be transmitted. The serial

number is meant to be unique for every transmitter.

3.6

User Data

The 64-bit user EEPROM can be reprogrammed and

read at any time using the IFF interface.

FIGURE 3-1:

SEED TRANSMISSION

Note:

If both SEED and TMPSD are set, IFF2

mode is enabled.

All examples shown with XSER = 1 & SEED = 1

When S[2:0] = 111, the 3-second delay is not applicable:

Que [1:0], CRC [1:0],

SEED_3 (12 bits)

SEED_2

SEED_1

SEED_0

Data transmission direction

For S[2:0] = 011 before the 3-second delay:

16-bit Data Word

16-bit Counter

Encrypt

SER_1

SER_0

Encrypted Data

For S[2:0] = 011 after the 3-second delay (Note 1):

Data transmission direction

Note 1: For Seed Transmission, SEED_3 and SEED_2 are transmitted instead of SER_1 and SER_0, respectively.

SEED_3 (12 bits)

SEED_2

SEED_1

SEED_0

Data transmission direction

Que [1:0], CRC [1:0]

Que [1:0], CRC [1:0],

*Patents have been applied for.