HCS515_11 Datasheet, PDF (12/38 Pages) Microchip Technology – KEELOQ® Code Hopping Decoder stand-alone decoder

HCS515
4.2.7 ERASE ALL
The erase all command (Figure 4-6) erases all the
transmitters in the decoder. After the command and two
dummy bytes are clocked in, the clock line must be
asserted to activate the command. After a successful
completion of an erase all command, the data line is
asserted until the clock line goes low.
FIGURE 4-6: ERASE ALL
CLK
μC DATA
LSB
MSB LSB
MSB LSB
TERA
TACK
TRESP
MSB
TACK2
Decoder DATA
START Command Command Byte
Subcommand Byte
Dummy Byte
A
B
C
D
E
Acknowledge
F
4.2.8 ACTIVATE LEARN
The activate learn command (Figure 4-7) 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 4-8).
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 8 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 microcon-
troller 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.
Upon reception of the second transmission, the
decoder will respond with a learn status message
(Figure 4-9).
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, 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 trans-
mitter 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.
FIGURE 4-7: LEARN MODE ACTIVATION
CLK
μC DATA
LSB
MSB LSB
MSB LSB
TLRN
TACK
TRESP
MSB
TACK2
ecoder DATA
START Command
A
B
Command Byte
C
Dummy Byte
Dummy Byte
D
E
Acknowledge
F
DS40183E-page 12
© 2011 Microchip Technology Inc.