ELM624P データシートの表示（PDF） - Elm Electronics
部品番号
コンポーネント説明
メーカー
ELM624P Datasheet PDF : 16 Pages
| |||
ELM624
The Control L Data Format
In a ‘Control L’ or ‘LANC’ system, data is sent in
groups of eight bytes at a time, with all groups
repeating at either a 50Hz or a 60Hz rate depending
on where the system was purchased. Information
flows both ways using these eight bytes, with the first
four bytes usually being sent to the device being
controlled, and the remaining four being responses
from that device. Except for voltage level differences,
each byte is transferred in a manner which is identical
to that of the RS232 standard (that is common
throughout the computer industry). If the signal were
inverted, it could likely be input directly to a computer’s
serial port, and read as 9600 baud data. The data
could not be displayed directly by a terminal program
however, as it would be raw data and would have to
be converted to ASCII characters for display on a
screen.
While receiving data is relatively easy, the sending
of data to the controlled device is not. All transfers
must be sent in synchronism with the eight pulses
which are generated by the controlled device, and this
must be done with only a few microseconds of error.
Responding to a real-time signal such as this is very
difficult to do with many modern computer systems
due to the complexity of their operating systems. The
ELM624 can handle this easily however, as it is a
dedicated device. It receives the data from the
computer or PDA, checks for errors, then synchronizes
to the time signals and sends the data out. Data
received during the frame is reformatted and sent to
the controlling computer during the next frame. There
is an idle period between frames (typically about
5msec) when very little activity actually occurs, so the
IC uses this to prepare for the next frame, and to
monitor the RS232 Rx line for any new commands.
Occasionally, the ELM624 will be asked to send a
Control L signal on the bus, and it will be unable to
sense any synchronizing pulses being sent by the
controlled device. If the device is not providing these
pulses for any reason, the ELM624 will simply display
‘NO SYNC’, and will return to the ready mode awaiting
another command. If this error does occur, check your
connecting cables and power supplies. The Check
Sync (AT CS) command can be used to verify that all
is well before proceding.
The figure below is representative of a typical
frame of data that is sent on the Control L or LANC
bus. Commands to the device (from the ELM624) are
sent during the first half of the frame, while the second
half (the last four bytes) are generally for feedback
from the controlled device. Often, four bytes are not
enough for the device to send all of the information, so
data is multiplexed over several frames. An example of
this is the time codes which will be discussed in the
next section.
one data group (8 bytes)
to the controlled device
from the controlled device
Figure 2. Control L data grouping
idle time
the next group starts
ELM624DSD
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
8 of 16
Share Link: 