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參數(shù)資料
| 型號： | MC14497P |
| 廠商： | MOTOROLA INC |
| 元件分類： | 搖控器 |
| 英文描述： | Digital Signal Processor,Military Known Good Die 0-XCEPT -55 to 125 |
| 中文描述： | INFRARED, TRANSMITTER IC, PDIP18 |
| 封裝： | PLASTIC, DIP-18 |
| 文件頁數(shù)： | 3/8頁 |
| 文件大?。?/td> | 166K |
| 代理商： | MC14497P |
MC14497
MOTOROLA
3
CIRCUIT OPERATION
The transmitter sends a 6–bit, labelled A (LSB) to F (MSB),
binary code giving a total of 64 possible combinations or
code words. All of these channels are user selectable, ex-
cept the last two (where channel 63 is not sent while channel
62 is automatically sent by the transmitter at the end of each
transmission as an “End of Transmission” code).
In either mode, FSK or AM, the transmitted signal is in the
form of a bi–phase pulse code modulation (PCM) signal. The
AM coding is shown in Figure 1.
BIT–n
f1
f1
“0”
“1”
Figure 1. AM Coding
AM
In the AM mode, f1 is a train of pulses at the modulating
frequency of 31.25 kHz for a reference frequency of 500 kHz.
In the FSK mode, two modulating frequencies are used as
shown in Figure 2.
BIT–n
f2
f3
“0”
“1”
Figure 2. FSK Coding
f2
f3
FSK
In this mode, f3 is 50 kHz and f2 is 41.66 kHz for a refer-
ence frequency of 500 kHz.
The keyboard can be a simple switch matrix using no ex-
ternal diodes, connected to the four scanner inputs (A1 – A4)
and the eight row input (E1 – E8). Under these conditions,
only the first 32 code words are available since bit–F is al-
ways at logical 0. However, a simple 2–pole changeover
switch, in the manner of a typewriter “shift” key (switch FK3 in
the Block Diagram) can be used to change the polarity of
bit–F to give access to the next full set of 32 instructions.
An alternative method of accessing more than 32 instruc-
tions is by the use of external diodes between the address
inputs (see Figure 3). These have the effect of producing
“phantom” address inputs by pulling two inputs low at the
same time, which causes bit–F to go high (i.e., to logical 1).
By interconnecting only certain address inputs it is possible
to make an intermediate keyboard with between 32 and 64
keys.
The other two switches in the Block Diagram (FK1 and
FK2) change the modulation mode. Closing FK1 changes
the modulation from FSK to AM and the start–bit polarity.
Closing FK2 changes the start–bit to a logical 0.
The full range of options available is illustrated in Table 1.
Table 1.
Start
Bit
Modulation
Bit–F
Channels
E9 = Open
1
FSK
0
0 – 31
E9 = A1 (FK1)
1
AM
0
0 – 31
E9 = A2 (FK2)
0
FSK
0
0 – 31
*
E9 = A3 (FK3)
1
FSK
1
32 – 61
E9 = A1
A2
0
AM
0
0 – 31
E9 = A1
A3
1
AM
1
32 – 61
E9 = A2
A3
0
FSK
1
32 – 61
*
E9 = A1
A2
A3
0
AM
1
32 – 61
* Not allowed.
One of the transmitter’s major features is its low power
consumption (in the order of 10
μ
A in the idle state). For this
reason, the battery is perpetually in circuit. It has in fact been
found that a light discharge current is beneficial to battery
life.
In its active state, the transmitter efficiency is increased by
the use of a low duty cycle which is less than 2.5% for the
modulating pulse trains.
While no key is pressed, the circuit is in its idle state and
the reference oscillator is stopped. Also, the eight address in-
put lines are held high through internal pull–up resistors.
As soon as a key is pressed, this takes the appropriate ad-
dress line low, signaling to the circuit that a key has been se-
lected. The oscillator is now enabled. If the key is released
before the code word has been sent, the circuit returns to its
idle state. To account for accidental activation of the transmit-
ter, the circuit has a built–in reactive time of approximately
20 ms, which also overcomes contact bounce. After this
delay, the code word will be sent and repeated at 90 ms inter-
vals for as long as the key is pressed. As soon as the key is
released, the circuit automatically sends channel 62, the
“End of Transmission” (EOT) code. The transmitter then re-
turns to its idle state.
The differences between the two modulation modes are il-
lustrated in Figure 4. However, it should be noted that in the
AM mode, each transmitted word is preceded by a burst of
pulses lasting 512
μ
s. This is used to set up the AGC loop in
the receiver’s preamp. In the FSK mode, the first frequency
of the first bit is extended by 1.5 ms and the AGC burst is
suppressed. In either mode, it is assumed that the normal
start–bit is present.
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