TRC1300, TRC1315
MARCSTAR
I E/D
REMOTE CONTROL ENCODER/DECODERS
SLWS011D – AUGUST 1996 – REVISED JANUARY 1997
13
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
encoder mode (continued)
Two or more buttons can be pressed at the same time to activate additional functions. Since it is not possible
to press them at
exactly the same time, a form of debouncing ensures that only a single function code is received
as valid. Function data is sent in two 12-bit packets. The first function-data packet is derived from the first sample
of the buttons (S1) at the beginning of the frame, and the second function-data packet is derived from the second
sample of the buttons (S2) immediately after the 40-bit security code (see Figure 5). This gives an effective 168
data-clock debounce time because the MARCSTAR I E/D, configured as a decoder, activates function outputs
only when the two function data packets in the frame are identical. When valid function data has been received
in the first packet but the second packet in a frame contains different function data (caused by a second button
being down at sample 2 time), both data packets are discarded and the decoder function outputs remain in their
previous state.
VRC/TX1 –
VRC/TX 4
(active low)
DIN/DOUT
360 Frames
48 Bits
40 Symbols (120 bits)
Precode
(Sync)
Security Code
Frame Data (193 Bits)
S1 – Button
Sample 1
150 Zero Bits
One Complete Frame (343 Bits)
4 Symbols
(12 Bits)
Data Packet 1
Data Packet 2
4 Symbols
(12 Bits)
Dummy Pulse (1 Bit)
Function Data (24 Bits)
Blank-Time (150 Bits)
25 Bits
S2 – Button Sample 2
Figure 5. Transmitted Data Format
If the user is holding buttons B1 and B2 on the transmitter down, both the first button sample (S1) and the second
button sample (S2) should find both buttons down as the next frame is prepared and sent. So, the
next frame
that is transmitted should contain the same function data in both the first and the second function data packets,
and the decoder activates function outputs 1 and 2. So as an example, if transmitter button B1 activates the door
locks, button B2 activates the alarm, and both button B1
and button B2 pressed at the same time activates the
trunk lock, the MARCSTAR sampling/debouncing function prevents the door locks and alarm from being
activated when the user intent is to activate only the trunk lock.