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參數(shù)資料
| 型號(hào)： | LM1872N |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 消費(fèi)家電 |
| 英文描述： | Radio Control Receiver/Decoder |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PDIP18 |
| 封裝： | PLASTIC, DIP-18 |
| 文件頁(yè)數(shù)： | 5/19頁(yè) |
| 文件大?。?/td> | 371K |
| 代理商： | LM1872N |
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Circuit Description
The following discussion is best understood by referring to
Figures 2, 3, 4, and 5.
SYSTEM ENCODING AND DECODING SCHEME
For the transfer of analog information, the LM1871/LM1872
system uses conventional pulse width modulation (PWM). In
applying this technique, the RF carrier is interrupted for
short fixed intervals (t
M
in Figure 2 ) with each interval fol-
lowed by variable width pulses (t
CH
) so as to define multiple
variable time spans (t
M
a
t
CH
) occurring in serial fashion.
Synchronization is accomplished by allowing one of the
transmitted variable pulse widths (t
SYNC
) to exceed the du-
ration (t’
SYNC
) of a receiver-based timer, thus allowing the
receiver to recognize this pulse for synchronization purpos-
es. Taken in sequence, this collection of pulses constitutes
a single frame period (t
F
).
The LM1871 transmitter is equipped to transmit up to six
channels which the companion LM1872 receiver uses to
derive 2 analog and 2 digital channels. The receiver de-
codes the demodulated RF waveform from the transmitter
by negative edge triggering a cascade of three binary divid-
ers called the A, B, and C toggle flip-flops (Figure 4 ). By
‘‘examining’’ all three flip-flop outputs simultaneously, up to
6 unique channel time intervals could be identified and re-
covered. Only the first two channels are actually decoded
however and outputted by the receiver, the rest being used
for identification of two digital (ON/OFF) channels. In pass-
ing digital information, a pulse count modulation scheme is
used whereby different quantities of channel pulses are
transmitted by varying the number of fixed width channels
following the two variable width analog channels 1 and 2
(see Figure 3 ).
TL/H/7912–5
FIGURE 2. RX Timing Waveforms
LM1871
TX
LM1872
RX
Pin Conditions
Transmitted Waveform
Binary
Pulse Count
Digital Outputs
Pin 5 (CH A)
Pin 6 (CH B)
CH A
CH B
OPEN
OPEN
100
OFF
OFF
TL/H/7912–6
GND
OPEN
101
ON
OFF
TL/H/7912–7
OPEN
GND
110
OFF
ON
TL/H/7912–8
GND
GND
111
ON
ON
TL/H/7912–9
FIGURE 3. Digital Channel Encoding and Decoding via Pulse Count Modulation
5
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