HCS500-ISM MICROCHIP [Microchip Technology], HCS500-ISM Datasheet - Page 11

• Manufacturer Part Number: HCS500-ISM
• Description: KEELOQ CODE HOPPING ENCODER
• Manufacturer: MICROCHIP [Microchip Technology]

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
FIGURE 4-6:
FIGURE 4-7:
FIGURE 4-8:
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.
Decoder DATA
CLK
Decoder
Data
1997 Microchip Technology Inc.
C DATA
CLK
A
ACTIVATE LEARN
T
CLA
Communications Request
A
Start Command
T
DHI
LEARN MODE ACTIVATION
LEARN STATUS MESSAGE AFTER FIRST TRANSMISSION
LEARN STATUS MESSAGE AFTER SECOND TRANSMISSION
T
CA
Decoder
Data
B
T
T
CLL
LSB
CLH
CLK
B
0
Command Byte
T
A
CLKL
T
CLA
OVR RSLT
Command Request
MSB
T
DHI
T
CA
0
C
T
LSB
0
CLKH
Preliminary
T
T
CLL
CLH
Learn Status Bits
0
Dummy Byte
B
0
0
T
0
MSB
CLKL
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
T
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.
CNT0
0
Status Byte
D
0
LSB
T
CNT3
0
CLKH
Dummy Byte
TX0
0
T
0
MSB
DS
TX3
T
LRN
0
Ci
C
E
RX0
RX1
HCS500
Decoded Tx
T
Acknowledge
ACK
DS40153B-page 11
T
RESP
T
RX62
ACK
2
RX63
Cii
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