參數(shù)資料
型號(hào): MC44107
廠商: Motorola, Inc.
英文描述: IR Remote Control Transmitter
中文描述: 紅外遙控發(fā)射器
文件頁數(shù): 3/8頁
文件大?。?/td> 168K
代理商: MC44107
MC44107
MOTOROLA
3
CIRCUIT OPERATION
The transmitter emits a 9–bit, labelled A (LSB) to I (MSB),
binary code able to encode 512 commands organized as
8 pages of 64 commands. All of these commands are user
selectable except the last command (511) which is used as
an SST, Start/Stop Transmission code.
Each bit of the transmitted signal is in the form of a biphase
pulse code modulated (PCM) signal, whose coding is shown
in Figure 1.
Figure 1. Signal Coding
BIT–n
‘0’
AM
‘1’
f1*
f1*
* f1 is a train of pulses at the
carrier frequency
÷
16.
The keyboard can be a simple switch matrix, connected
between the eight row inputs (1 to 8) and the seven column
outputs (B to H). VSS acts as the eight column line to give the
full complement of 64 commands per page. The maximum
“ON” resistance of the keyboard must be limited to 500
.
Page access is accomplished by connecting, by means of
a key, the page input to one of the seven column outputs or
by leaving the input circuit open.
One of the circuit’s major features is its low standby cur-
rent consumption — typically less than 1
μ
A. For this reason
the battery may be left continuously in circuit.
As soon as a key is selected, the circuit switches to its ac-
tive mode and enables the oscillator. To allow for accidental
activation and/or key bounce, the circuit requires that the key
is held for a minimum delay of tkey, which in the case of a
500 kHz oscillator is 65.6 ms. After this delay the column/
row/page command, consisting of a string of messages (see
Figure 2), appropriate to the key selected will be transmitted
and repeated until the key is released.
Any page key required must be selected before, and held
during, the selection of the column/row matrix key. If this se-
quence is not followed, the circuit will default to the appropri-
ate command between 0 and 63. If two or more page keys
are accidentally held down, only the first one pressed will be
detected.
A command consists of several messages. Each com-
mand starts with the message 511 (SST) followed by the
message appropriate to the key selected. These messages
are repeated until the key is released. The final message is
always followed by the SST message, 511.
Every message consists of a pre–bit, a pre–bit pause, a
start–bit, and nine data bits, where the pre–bit and the start–
bit are always logical “1”. The pre–bit allows for the set up of
the AGC loop in the receiving preamplifier. The truth tables
for data bits are given in Tables 1 and 2, while Figure 2
shows the timing relationships between the commands,
messages, and modulation.
In the event of accidental multi–key operation, the circuit
will react in one of three ways, depending on the combination
of the keys selected.
When two or more keys are connected to the same row in-
put and any column output except A, the command appropri-
ate to the first key selected will be transmitted until that key is
released. After the SST code has been transmitted, assum-
ing another key is still selected, the command appropriate to
that key will be transmitted. If the other key has been re-
leased in the meantime, the circuit will revert to standby.
If two keys are selected in the same row with one being
connected to column A, any transmission will terminate with
the SST code and then the circuit will transmit the command
appropriate to the key connected to column A.
In the case where two or more keys connected to the same
column are selected, the circuit reacts in a normal manner to
the first key activated. Upon selection of the second key, the
SST code is transmitted and the circuit will revert to the
standby mode. Only when the multi–key condition is re-
leased and a single key is selected will the circuit resume op-
eration, as previously described.
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