HCS410 Datasheet, PDF (10/36 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER AND TRANSPONDER

HCS410
2.2.2 TRANSMISSION DATA MODULE
The Data Modulation Format is selectable between
Pulse Width Modulation (PWM) format and Manchester
encoding. Both formats are preceded by a preamble
and synchronization header, followed by the 69-bits of
data. Manchester encoding has a leading and closing
‘1’ for each code word.
The same code word is continuously sent as long as
the input pins are kept high with a guard time separat-
ing the code words. All of the timing values are in mul-
tiples of a Basic Timing Element (TE), which can be
changed using the baud rate option bits.
FIGURE 2-10: TRANSMISSION FORMAT—MANCH = 0
TOTAL TRANSMISSION:
1 CODE WORD
Preamble Sync Encrypt Fixed
Guard Preamble Sync Encrypt
CODE WORD:
LOGIC "0"
LOGIC "1"
TE
BIT
TE
12 45 6
Preamble
13579
14 15 16 2 4 6 8 10
Sync
Code Word
Encrypted
TX Data
Fixed Code
Data
GTiumaerd
FIGURE 2-11: TRANSMISSION FORMAT—MANCH = 1
TOTAL TRANSMISSION:
1 CODE WORD
Preamble Sync Encrypt Fixed
Guard Preamble Sync Encrypt
TE
CODE WORD:
LOGIC "0"
BPW
LOGIC "1"
12
456
Preamble
Start bit
13
14 15 16 ^{2 4}
Sync
Encrypted
Data
CODE WORD
Stop bit
Fixed Code
Data
Guard
Time
DS40158C-page 10
Preliminary
© 1997 Microchip Technology Inc.