HCS370_11 Datasheet, PDF (12/42 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder Four selectable baud rates

HCS370
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)
Hopping Code Portion (32 Bits)
BUT
4 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)
Hopping Code Portion (32 Bits)
BUT
4 Bits
DISC
8 Bits
Synchronization
Counter
20 Bits
19
0
S2 S1 S0 S3
3.2.3.1 Low Voltage Detector Status (VLOW)
A low battery voltage detector onboard the HCS370
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 checked on
the first preamble pulse of each code word with the
LED momentarily turned off. The VLOW bit is transmit-
ted in each code word so the decoder can give an indi-
cation to the user that the transmitter battery is low.
Operation of the LED changes as well to further indi-
cate 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, like a Schmitt Trigger.
This will effectively hold the VLOW bit high until the bat-
tery is replaced. If the Low Voltage Latch is enabled,
then the low TE after the first preamble pulse can
stretch by 4 ms one time as the latch changes state.
Transmission Direction LSB First
DS41111E-page 12
2011 Microchip Technology Inc.