|
HCS410 Datasheet, PDF (20/36 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 ï¬xed code word as part of a different key genera-
tion/tracking process or purely as a ï¬xed 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 signiï¬cant 32-bits of the seed are used as the
transport code. The transport code is used to write-pro-
tect the serial number, conï¬guration 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 conï¬guration 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.
*Patents have been applied for.
DS40158C-page 20
Preliminary
© 1997 Microchip Technology Inc.
|
▷ |