HCS410_01 Datasheet, PDF (19/36 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder

HCS410
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 seconds,
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.
Note: If both SEED and TMPSD are set, IFF2
mode is enabled.
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
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)
VLOW, S[2:0]
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
Que [1:0], CRC [1:0] _{SER_1}
+ VLOW, S [2:0]
SER_0
For S[2:0] = 011 after the 3-second delay (Note 1):
Encrypted Data
Data transmission direction
Que [1:0], CRC [1:0], SEED_3 (12 bits)
VLOW, S [2:0]
SEED_2
SEED_1
SEED_0
Data transmission direction
Note 1: For Seed Transmission, SEED_3 and SEED_2 are transmitted instead of SER_1 and SER_0, respectively.
 2001 Microchip Technology Inc.
Preliminary
DS40158E-page 19