HCS500 datasheet(12/40 Pages) MICROCHIP

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HCS500

DS40153D-page 12

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 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.

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,

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 4-6:

LEARN MODE ACTIVATION

FIGURE 4-7:

LEARN STATUS MESSAGE AFTER FIRST TRANSMISSION

FIGURE 4-8:

LEARN STATUS MESSAGE AFTER SECOND TRANSMISSION

Decoder

MSB

Command Byte

Start Command

LSB

TLRN

Dummy Byte

CLK

μC DATA

Acknowledge

MSB

LSB

MSB

LSB

TACK

TRESP

TACK2

DATA

Command Request

TCLKL

TCLKH

TCA

TDS

TCLL

TDHI

TCLA

TCLH

CLK

Decoder

Status Byte

Data

Communications Request

TCLKL

TCLKH

TCA

TDS

Cii

TCLL

TDHI

TCLA

TCLH

CLK

Decoder

TX0

TX3

RX63

OVR RSLT

CNT0

CNT3

RX0

RX1

RX62

Learn Status Bits

Decoded Tx

Data

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