HCS370 Datasheet, PDF (15/36 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS370
FIGURE 4-3:
VARIABLE PULSE WIDTH MODULATION (VPWM)
LOGIC “0”
TE
VPWM BIT ENCODING:
on Transition Low to High
on Transition High to Low
TBP
2XTE
LOGIC “0”
TE
LOGIC “1”
TE
TBP
LOGIC “1”
TE TE
12
TBP
TBP
16
2XTE
31xTE 50% Preamble
10xTE Header Encrypted Portion
Fixed Code Portion
Guard
Time
FIGURE 4-4: PULSE POSITION MODULATION (PPM)
TE TE TE
12
LOGIC "0"
LOGIC "1"
START bit
TBP
16
TBP
3 X TE
STOP bit
31xTE 50% Preamble
10xTE Header
Encrypted Portion Fixed Code Portion
Guard
Time
In addition to the Modulation Format, Guard Time, and
Baud Rate, the following options are also available to
change the transmission format:
• If the START/STOP Pulse Enable (STEN) config-
uration option is enabled, the HCS370 will place a
leading and trailing ‘1’ on each code word. This is
necessary for modulation formats such as
Manchester and PPM to interpret the first and last
data bit.
• A wake-up sequence can be transmitted before
the transmission starts. The wake-up sequence is
configured with the Wake-up (WAKE) configura-
tion option and can be disabled or set to 50 ms,
75 ms, or 100 ms of pulses as indicated in
Figure 4-5.
• The WAKE option is the same for both Encoder 1
and Encoder 2.
FIGURE 4-5: WAKE-UP ENABLE
TE TE
WAKE-UP = 75 ms
TE 2TE
WAKE-UP = 50 ms
TE
5TE
WAKE-UP = 100 ms
TG
TG
WAKE-UP CODE
CODE
Guard Time = 6.4 ms, 51.2 ms, or 102.4 ms
2002 Microchip Technology Inc.
Preliminary
DS41111D-page 15