HCS412 Datasheet, PDF (22/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

HCS412
4.3.2 READ
The transponder reader sends one of seven possible
read commands indicating which 16-bit EEPROM word
to retrieve (Table 4-4). The HCS412 retrieves the data
and returns the 16-bit response.
Each Read response is preceded by a 1LFTE low
START pulse and ‘01b’ preamble (Figure 4-4).
TABLE 4-4: LIST OF READ COMMANDS
The following locations are available to read:
• The 64-bit general purpose user EEPROM.
(USER[3:0]).
• The 32-bit serial number (SER[1:0]). The serial
number is also transmitted in each code hopping
transmission.
• The16-bit Configuration word containing all non-
security related options.
Command
Description
Expected data In
Response
00001
00010
00011
00100
00101
00110
00111
Read Configuration word
Read low serial number
Read high serial number
Read user EEPROM 0
Read user EEPROM 1
Read user EEPROM 2
Read user EEPROM 3
None
None
None
None
None
None
None
16-bit Configuration word
Lower 16 bits of serial number (SER0)
Higher 16 bits of serial number (SER1)
16 Bits of User EEPROM USR0
16 Bits of User EEPROM USR1
16 Bits of User EEPROM USR2
16 Bits of User EEPROM USR3
FIGURE 4-4: READ
Activate
Field ^ACK
Delay to
Command
TPU
TATO
Command
Delay until
Response
16-bit Response
TRT
01b Preamble
6 LFTE
01
ACK
Communication from reader to HCS412
Communication from HCS412 to reader
2 LFTE
Start
Command
1 LFTE
Start
16-bit
Response
4.3.3 WRITE
The transponder reader sends one of seven possible
write commands (Table 4-5) indicating which 16-bit
EEPROM word to write to. The 16-bit data to be written
follows the command. The HCS412 will attempt to write
the value into EEPROM and respond with an Acknowl-
edge sequence if successful.
The following locations are available to write:
• The 64-bit general purpose user EEPROM.
(USER[3:0]) (Figure 4-6).
• The 32-bit serial number (SER[1:0]). The serial
number is also transmitted in each code hopping
transmission (Figure 4-5).
• The16-bit Configuration word containing all non-
security related configuration options. If the con-
figuration is written, the device must be RESET
before the new settings take effect (Figure 4-5).
A Transport Code, write access password, protects the
serial number and configuration word from undesired
modification. For these locations the reader must follow
the WRITE command with the appropriate 28-bit trans-
port code, then the 16 bits of data to write. Only a cor-
rect match with the transport code programmed during
production will allow write access to the serial number
and configuration word (Figure 4-5).
The delay to a successful write Acknowledge will vary
depending on the number of bits changed.
DS41099C-page 22
Preliminary
© 2002 Microchip Technology Inc.