hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 12

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

HCS500
4.2.7
The activate learn command (Figure 4-6) is used to
activate a transmitter learning sequence on the
decoder. The command consists of a Command mode
activation sequence, a command byte, and two dummy
bytes. The decoder will respond by taking the data line
high to acknowledge that the command was valid and
that learn is active.
Upon reception of the first transmission, the decoder
will respond with a learn status message (Figure 4-7).
During learn, the decoder will acknowledge the recep-
tion of the first transmission by taking the data line high
for 60 ms. The controlling microcontroller can clock out
at most eight bits, which will all be zeros. All of the bits
of the status byte are zero, and this is used to distin-
guish between a learn time-out status string and the
first transmission received string. The controlling micro-
controller must ensure that the clock line does not go
high 60 ms after the falling edge of the data line, for this
will terminate learn.
FIGURE 4-6:
FIGURE 4-7:
FIGURE 4-8:
DS40153C-page 12
CLK
Decoder
Data
Decoder
C DATA
DATA
CLK
T
A
CLA
A
ACTIVATE LEARN
Start Command
Communications Request
T
DHI
LEARN MODE ACTIVATION
LEARN STATUS MESSAGE AFTER FIRST TRANSMISSION
LEARN STATUS MESSAGE AFTER SECOND TRANSMISSION
T
CA
Decoder
Data
B
T
LSB
T
CLL
CLH
CLK
Command Byte
B
0
T
CLKL
T
CLA
OVR RSLT 0
A
Command Request
MSB
T
DHI
T
CA
C
LSB
T
0
CLKH
T
T
CLL
CLH
Learn Status Bits
Dummy Byte
0
B
0
0
0
MSB
T
1
Upon reception of the second transmission, the
decoder will respond with a learn status message
(Figure 4-8).
The learn status message after the second transmis-
sion consists of the following:
• 1 START bit.
• The function code [S3:S0] of the message is zero,
• The RESULT bit indicates the result of the learn
• The OVR bit will indicate whether an exiting trans-
• The [CNT3…CNT0] bits will indicate the number
• The [TX3…TX0] bits indicate the block number
DS
indicating that this is a status string.
sequence. The RESULT bit is set if successful
and cleared otherwise.
mitter is over written. The OVR bit will be set if an
existing transmitter is learned over.
of transmitters learned on the decoder.
used during the learning of the transmitter.
T
CNT0
0
CLKL
D
Status Byte
LSB
0
T
CLKH
CNT3
Dummy Byte
0
TX0
0
MSB
0
T
TX3
LRN
T
0
DS
2002 Microchip Technology Inc.
E
RX0
C
Ci
RX1
T
Decoded Tx
Acknowledge
ACK
RX62
RX63
T
RESP
T
F
Cii
ACK
2