HCS500_15 Datasheet, PDF (13/42 Pages) Microchip Technology – KEELOQ® Code Hopping Decoder

HCS500
4.2.7 ACTIVATE LEARN
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
reception 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 distinguish between a learn time-out status string
and the first transmission received string. The
controlling microcontroller 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: LEARN MODE ACTIVATION
CLK
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
transmission consists of the following:
• 1 Start bit.
• The function code [S3:S0] of the message is zero,
indicating that this is a status string.
• The RESULT bit indicates the result of the learn
sequence. The RESULT bit is set if successful
and cleared otherwise.
• The OVR bit will indicate whether an exiting
transmitter is over written. The OVR bit will be set
if an existing transmitter is learned over.
• The [CNT3…CNT0] bits will indicate the number
of transmitters learned on the decoder.
• The [TX3…TX0] bits indicate the block number
used during the learning of the transmitter.
TLRN
TACK
TRESP
C DATA
LSB
MSB LSB
MSB LSB
MSB
TACK2
Decoder
DATA
Start Command
A
B
Command Byte
C
Dummy Byte
Dummy Byte
D
E
Acknowledge
F
FIGURE 4-7:
LEARN STATUS MESSAGE AFTER FIRST TRANSMISSION
TCA
TCLL
TCLKH
TDS
CLK
TCLA
TCLH
TCLKL
Decoder
Data
TDHI
0
Command Request
A
B
0 00 0 0 00
Status Byte
C
FIGURE 4-8:
CLK
TCLA
LEARN STATUS MESSAGE AFTER SECOND TRANSMISSION
TCA
TCLL
TCLKL
TCLKH
TDS
TCLH
TDHI
Decoder
Data
0 OVR RSLT 0
Communications Request
A
B
0 0 0 1 CNT0
Learn Status Bits
CNT3 TX0
TX3 RX0 RX1
RX62 RX63
Decoded Tx
Ci
Cii
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DS40000153E-page 13