hcs473 Microchip Technology Inc., hcs473 Datasheet - Page 15

• Manufacturer Part Number: hcs473
• Description: Code Hopping Encoder And Transponder
• Manufacturer: Microchip Technology Inc.

3.1.3
The data modulation format is selectable between
Pulse Width Modulation (PWM) and Manchester using
the modulation select (MSEL) configuration option.
Regardless of the modulation format, each code word
contains a leading preamble and a synchronization
header to wake the receiver and provide synchroniza-
tion events for the receive routine. Each code word also
contains a trailing guard time to separate code words.
Manchester encoding further includes a leading data ‘1’
START pulse and closing 1 RFT
each data block.
FIGURE 3-3:
FIGURE 3-4:
 2002 Microchip Technology Inc.
TOTAL TRANSMISSION:
TOTAL TRANSMISSION
CODE HOPPING MODULATION
FORMAT
Preamble
PWM TRANSMISSION FORMAT (MSEL = 0)
MANCHESTER TRANSMISSION FORMAT (MSEL = 1)
Preamble
START bit
Header
:
E
bit 0 bit 1 bit 2
STOP pulse around
Preamble Sync Encrypt
Preamble Sync Encrypt
Encrypted
Portion
LOGIC "0"
LOGIC "1"
Preliminary
Header
CODE WORD
1 CODE WORD
1 CODE WORD
CODE WORD
LOGIC “0”
LOGIC “1”
Fixed
Fixed
The same code word repeats as long as the same input
pins remain active, until a timeout occurs or a delayed
seed transmission is activated.
The modulated data timing is typically referred to in
multiples of a basic Timing Element (RFT
because the DATA pin output is typically sent through a
RF transmitter to the decoder or transponder reader.
RFT
Baud
(Section 3.1.4.13).
T
Encrypted
E
Portion
Fixed Code
E
T
T
Portion
E
E
may be selected using the RF Transmission
Guard
Guard
Rate
T
T
E
E
Preamble Sync Encrypt
Preamble Sync Encrypt
(RFBSL)
STOP bit
Fixed Code
Portion
Guard
Time
configuration
HCS473
DS40035C-page 13
Guard
Time
E
). ‘RF’ T
option
E