HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 14

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

HCS412
The Code Word Blanking Enable (CWBE) option may
be used to reduce the average power of a transmission
by transmitting only every second or every fourth code
word
determined in conjunction with the baud rate selection
bit RFBSL (Table 3-7).
FIGURE 3-7:
TABLE 3-7:
3.4.4
The HCS412’s Delayed Increment feature advances
the synchronization counter by 12 a period of T
the encoder activation occurs, for additional security.
The next activation will show a synchronization counter
increase of 13, not 1.
If the active button is released before the time-out T
has elapsed, the device stops transmitting but remains
powered for the duration of the time-out period. The
device will then advance the stored synchronization
counter by 12 before powering down.
If the active button is released before the time-out T
has elapsed and another activation occurs while wait-
ing out the time-out period, the time-out counter will
RESET and the resulting transmission will contain syn-
chronization counter value +1.
3.4.5
If the RFEN/S2/LC1 pin is configured as an RF enable
output, the pin’s behavior is coordinated with the DATA
pin to enable a typical PLL’s ASK or FSK mode.
DS41099C-page 14
RFBSL1:0
Note: If delayed increment is enabled, the QUE
(1 out of 2 transmitted)
(1 out of 4 transmitted)
(All words transmitted)
00b
01b
10b
11b
CWBE Disabled
CWBE Enabled
CWBE Enabled
(Figure 3-7).
RF Output Amplitude = A
DELAYED INCREMENT (DINC)
counter will not reset to 0 until timeout T
has elapsed.
PLL INTERFACE
CODE WORD BLANKING
CODE WORD BLANKING ENABLE (CWBE)
CWBE
X
0
1
0
1
0
1
This
selectable
2A
4A
PWM RFT
A
400 s
200 s
200 s
100 s
100 s
100 s
100 s
Code
Word
Code
Word
Code
Word
E
feature
TO
Manchester RFT
Code
Word
TO
after
Preliminary
TO
TO
is
800 s
400 s
400 s
200 s
200 s
200 s
200 s
Code
Word
Code
Word
Enabling the CWBE option may similarly allow the user
to transmit a higher amplitude transmission as the time
averaged power is reduced. CWBE effectively halves
the RF on-time for a given transmission so the RF out-
put power could theoretically be doubled while main-
taining the same time averaged output power.
The PLL Interface (AFSK) configuration option controls
the output as shown in Figure 3-8.
TABLE 3-8:
3.4.6
During normal operation (good battery), while transmit-
ting data the device’s LED pin will periodically be driven
low as indicated in Figure 3-9.
If the supply voltage drops below the trip point specified
by VLDWSEL, the LED pin will be driven low only once
for a longer period of time.
3.4.7
Enabling the Long Preamble configuration option
extends the first code word’s 50% duty cycle preamble
to a ‘long’ preamble time T
will be a square wave at the selected RFT
(Figure 3-10).
E
Code
Word
AFSK
0
1
LED OUTPUT
LONG PREAMBLE (LPRE)
Code
Word
Code
Word
Code
Word
Every fourth code word
Every other code word
Every other code word
PLL INTERFACE(AFSK)
Code
Word
All code words
All code words
All code words
All code word
Transmit...
2002 Microchip Technology Inc.
ASK PLL Setup
FSK PLL Setup
LPRE
Description
Code
Word
Code
Word
. The longer preamble
Code
Word
E