HCS370 Datasheet, PDF (13/36 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

3.3 Seed Code Word Data Format
A seed transmission transmits a code word that con-
sists of 60 bits of fixed data that is stored in the
EEPROM. This can be used for secure learning of
encoders or whenever a fixed code transmission is
required. The seed code word is identified by the func-
tion bits = 1111₂. The seed code word also contains the
status information (VLOW, CRC, and QUEUE). The
Seed code word format is shown in Figure 3-3. The
function code for seed code words is always 1111₂.
Seed code words for Encoder 1 and Encoder 2 can be
configured as follows:
• Enabled with the Seed Button Code (SDBT) con-
figuration option, or disabled if SDBT = 0000₂.
• If the Limited Seed (SDLM) configuration option is
set, seed transmissions will be disabled when the
synchronization counter is bigger than 127. Seed
transmissions remain disabled even if the 16/20-
bit counter rolls over to 0.
• The delay before the seed transmission is sent
can be set to 0.0s, 0.8s, 1.6s and 3.2s with the
Seed Time (SDTM) configuration option. When
SDTM is set to a value other than 0.0s, the
HCS370 will transmit a code hopping transmis-
sion until the selected time expires. After the
selected time expires, the seed code words are
transmitted. This is useful for the decoder to learn
FIGURE 3-3: SEED CODE WORD FORMAT
With QUEN = 1
Open Portion (Not Encrypted)
(9 bits)
QUE CRC VLOW Function
(2 Bits) (2 Bits) (1-Bit) (4 Bits)
Q1 Q0 C1 C0 1 1 1 1
HCS370
the serial number and the seed from a single but-
ton press.
• The button code for transmitting a seed code
word can be selected with the Seed Button
(SDBT) configuration option. SDBT bits 0 to 3 cor-
respond to button inputs S0 to S3. Set the bits
high for the button combination that should trigger
a seed transmission (i.e., If SDBT = 1010₂ then,
S3+S1 will trigger a seed transmission).
• The seed transmissions before the counter incre-
ments past 128 can be modified with the Seed
Mode (SDMD) configuration option. Setting this
bit for Production mode will cause the selected
seed button combination to first transmit a normal
hopping code word for the selected Minimum
Code words (MTX) and then at least MTX seed
code words until all buttons are released. This
mode is disabled after the counter reaches 128
even if the 16/20-bit counter rolls over to 0.
• The limit of 127 for SDLM or SDMD can be
reduced by using an initial counter value >0.
Note:
The synchronization counter only incre-
ments on code hopping transmissions.
The counter will not advance on a seed
transmission unless Seed Delay or Pro-
duction mode options are on.
SEED Code
(60 bits)
SEED
Transmission Direction LSB First
2002 Microchip Technology Inc.
Preliminary
DS41111D-page 13