HCS365 Datasheet, PDF (14/34 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS365
4.0 TRANSMITTED WORD
4.1 Transmission Modulation Format
The HCS365 transmission is made up of several code
words. Each code word contains a preamble, header,
and data. A code word is separated from another code
word by guard time. The Guard Time Select (GSEL)
configuration option can be set to 0 ms, 6.4 ms, 51.2
ms, or 102.4 ms.
All other timing specifications for the modulation for-
mats are based on a basic timing element (TE). This
Timing Element can be set to 100 µs, 200 µs, 400 µs or
800 µs with the Baud Rate Select (BSEL) configuration
option. The Header time can be set to 4TE or 10TE with
the Header Select (HSEL) configuration option. These
options can all be set individually for Encoder 1 and
Encoder 2.
There are four different modulation formats available
on the HCS365 that can be set individually for Encoder
1 or Encoder 2. The Modulation Select (MSEL) Config-
uration Option is used to select between:
• Pulse Width Modulation (PWM)
• Manchester (MAN)
• Variable Pulse Width Modulation (VPWM)
• Pulse Position Modulation (PPM)
FIGURE 4-1: PULSE WIDTH MODULATION (PWM)
TE TE TE
LOGIC "0"
LOGIC "1"
TBP
1
16
31xTE 50% Preamble
4-10
xTE ^{Encrypted Portion}
Header
Fixed Code Portion
Guard
Time
FIGURE 4-2: MANCHESTER (MAN)
12
START bit
bit 0 _{bit 1} bit 2
16
TE TE
LOGIC "0"
LOGIC "1"
TBP
STOP bit
31xTE 50% Preamble
4 xTE
Header
Encrypted Portion
Fixed Code Portion
Guard
Time
DS41109D-page 14
Preliminary
© 2002 Microchip Technology Inc.