HCS365 Datasheet, PDF (12/34 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS365
FIGURE 3-2: CODE WORD DATA FORMAT (20-BIT COUNTER)
With XSER=0, 20-bit Counter, QUEN=1
Status Information
(5 Bits)
Fixed Code Portion (32 Bits)
QUE CRC VLOW BUT
2 Bits 2 Bits 1-Bit 4 Bits
Q1 Q0 C1 C0 S2 S1 S0 S3
SERIAL NUMBER
(28 Bits)
BUT
4 Bits
Hopping Code Portion (32 Bits)
DISC
8 Bits
Synchronization
Counter
20 Bits
19
0
S2 S1 S0 S3
With XSER=1, 20-bit Counter, QUEN=0
Status Information
(3 Bits)
Fixed Code Portion (32 Bits)
CRC
2 Bits
C1 C0
VLOW
1-Bit
SERIAL NUMBER
(32 Bits)
BUT
4 Bits
Hopping Code Portion (32 Bits)
DISC
8 Bits
Synchronization
Counter
20 Bits
19
0
S2 S1 S0 S3
Transmission Direction LSB First
3.2.3.1 Low Voltage Detector Status (VLOW)
A low battery voltage detector onboard the HCS365
can indicate when the operating voltage drops below a
predetermined value. There are two options available
depending on the Low Voltage Trip Point Select
(VLOWSEL) configuration option. The two options pro-
vided are:
• A 2.2V nominal level for 3V operation
• A 3.2V nominal level for 5V operation
The output of the low voltage detector is transmitted in
each code word, so the decoder can give an indication
to the user that the transmitter battery is low. Operation
of the LED changes as well to further indicate that the
battery is low and needs replacing.
The output of the Low Voltage Detector can also be
latched once it has dropped below the selected value.
The Low Voltage Latch (VLOWL) configuration option
enables this option. If this option is enabled, the detec-
tor level is raised to 3V or 5V once a low battery voltage
has been detected. The original value is reinstated if
the VDD voltage is raised above this level, indicating
that a new battery has been installed.
The Low Voltage Latch (VLOWL) if enabled works sim-
ilar to a Schmitt Trigger. This will effectively hold the
VLOW bit high until the battery is replaced. If the Low
Voltage Latch is enabled, then the break after the first
preamble pulse can stretch by 4 ms one time as the
latch changes state.
DS41109D-page 12
Preliminary
© 2002 Microchip Technology Inc.