HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 12

• Manufacturer Part Number: HCS412I
• Description: KEELOQ Code Hopping Encoder and Transponder
• Manufacturer: MICROCHIP [Microchip Technology]

HCS412
FIGURE 3-4:
TABLE 3-4:
3.3
The data modulation format is selectable between
Pulse Width Modulation (PWM) and Manchester using
the Data Modulation (MOD) configuration option.
Regardless of the modulation format, each code word
contains a leading 50% duty cycle preamble and a syn-
chronization header to wake the receiver and provide
synchronization events for the receive routine. Each
code word also contains a trailing guard time, separat-
ing code words. Manchester encoding further includes
a leading and closing ‘1’ around each 69-bit data block.
The same code word repeats as long as the same input
pins remain active, until a time-out occurs or a delayed
seed transmission is activated.
TABLE 3-6:
DS41099C-page 12
Note 1: Refer to Table 3-1 for appropriate button activation of SEED transmissions.
RFBSL1:0
MSb
Note: SEED transmissions only allowed when appropriate configuration bits are set.
Q1 Q0 C1 C0
2 Bits
QUE
Shaded data included in CRC calculation
SEED
00b
01b
10b
11b
0
0
1
1
Transmission Data Modulation
2 Bits
CRC
SEED CODE WORD DATA FORMAT
SEED TRANSMISSION OPTIONS
TMPSD
BAUD RATE SELECTION (RFBSL)
CWBE
V
1-Bit
LOW
S2 S1 S0 LC0
X
0
1
0
1
0
1
0
1
0
1
4 Bits
BUT
PWM RFT
12 Most Sig Bits
400 s
200 s
200 s
100 s
100 s
100 s
100 s
SDVAL3
Limited SEED transmissions (Note 1) - temporarily enabled until the
SEED transmissions permanently disabled (2 key IFF enabled)
7 LSb’s of the synchronization counter wrap from 7Fh to 00h
E
SEED transmissions permanently enabled (Note 1)
Preliminary
Manchester RFT
SEED transmissions permanently disabled
800 s
400 s
400 s
200 s
200 s
200 s
200 s
SDVAL2
16 Bits
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
Rate (RFBSL) configuration option (Table 3-6).
TABLE 3-5:
* Enabling long preambles extends the first code
Preamble
word’s preamble to T
Header
Description
Period
Guard
E
Data
E
may be selected using the Transmission Baud
SDVAL1
PWM
16 Bits
TRANSMISSION
MODULATION TIMING
207
31*
10
46
Every fourth code word
Every other code word
Every other code word
LPRE
All code words
All code words
All code words
All code word
Transmit...
2002 Microchip Technology Inc.
Manchester
milliseconds.
142
31*
31
4
16 Least Sig Bits
69 Data bits
Transmitted
SDVAL0
LSb first.
E
). ‘RF’ T
RFT
Units
RFT
RFT
RFT
LSb
E
E
E
E
E