HCS473_13 Datasheet, PDF (27/68 Pages) Microchip Technology – KEELOQ® 3-Axis Transcoder

3.2.3.4 READ Command
The transponder reader follows the 3-bit READ com-
mand with one of eight possible 3-bit address options
indicating which 16-bit EEPROM word to retrieve
(Table 3-5) and a 2-bit CRC calculated over the com-
mand and address bits.
The HCS473 retrieves the data and returns the 16-bit
response by creating a 32-bit value containing two cop-
ies of the response (Figure 3-15).
RFRSP determines if the response will be transmitted
on the DATA pin. If enabled, the response will follow the
selected Encoder mode code hopping format with the
hopping code replaced with the 32-bit response. The
transmissions will contain a button code of ‘0000’.
HCS473
LFRSP determines if the response will be transmitted
on the LC pins. The LC pin response will be the 32-bit
result, modulated PPM format.
If both RFRSP and LFRSP are enabled, the HCS473
will send the response on the DATA pin immediately fol-
lowed by the PPM response on the LC pins. Refer to
Section 3.2.1.7 for further response path details.
The following locations are available to read:
• The 64-bit general purpose user EEPROM.
• The 32-bit serial number. The serial number is
also transmitted in each code hopping transmis-
sion.
• The16-bit device identifiers #1 and #2.
The next command must begin TCMD after the read
response.
FIGURE 3-15:
READ SEQUENCE (RF RESPONSE EXAMPLE)
Wake Sequence
or
Previous Command
Response
‘100₂’ 3 bits 2 bits
TCMD
TREAD
TCMD
CMD ADR CRC
RESPONSE
Command Address CRC
Optional Next
Command
Next
Command
TSF
Inductive In
(LC Pins)
RF Response
(DATA Pin)
TCMD
ACK
TCMD
LF must remain on if following
with consecutive command
or if waiting for LF response
TFINH
TREAD
RF Response (RFRSP=1)
TCMD
TCMD
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Preliminary
DS40035D-page 27