ELM624P データシートの表示（PDF） - Elm Electronics

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ELM624P

Control L (LANC) to RS232 Interpreter

Elm Electronics 

ELM624

Talking to Your LANC Device (cont’d)

looked something like these:

06122458

06324911

06420100

Comparing this to the other response, you can see

that the device is now in play mode (06), with the

time/counter still reading 00:01:11:49, as it has just

begun to play the tape. The 8 in the last position of the

first row indicates that (for this camera), there is a

‘memory mark’ here to show a significant spot on the

tape. This is how you would generally control a device

through LANC using computer control - issue a

command then monitor the status bytes until the

desired change has occurred. This way you can be

sure that the command was understood. Of course, if

you are manually controlling it from the keyboard, you

will know when the device has responded.

It is beyond the scope of this document to detail

the Control L standard in any more detail, but hopefully

this has been enough to get you started, and has

generated some ideas.

Talking to Many ELM624s - Using the Enable

The ELM624 provides an Enable input that can be

used to control whether the ELM624 pays attention to

the RS232 bus or not. This means that several devices

can share one data ‘channel’, while only those chosen

to do so will respond. In this way, controlling many

devices is not much different than controlling one,

except for the work involved in selecting the

appropriate ELM624, and deselecting the others.

RS232 data received at the Rx pin of the ELM624

while the Enable input is high will be used by the IC,

and any data that appears at that pin while the Enable

is low will be ignored. You can use this in order to

selectively send information to several devices that

share a common RS232 bus. The messages sent to

each device do not have to be sent all at once as a

complete string - you can send one byte to device 1, a

few bytes to device 2, a byte to device 3, etc., as long

as you return back to each device before their internal

20 second timer causes an abort on an incomplete

string receive. This is usually quite easy to do.

To ensure that the enable works properly when

sending commands to the ELM624, be sure to have it

at an active level before the RS232 byte’s start bit

begins, and maintain it at that active level until at least

the end of the stop bit. There is no such restriction for

controlling the ELM624’s Tx output. The IC will turn the

output line off within one bit time of the Enable going

inactive, so if you do not want to receive any more

from that device, simply bring the Enable line low.

The (continuous) flow of status messages can be

monitored periodically while doing other tasks through

the Enable control. For example, one could issue a

command to rewind the tape (10 36), then periodically

check for a ‘tape end stopped’ status byte (72) while

doing other functions with other devices. There is no

restriction on how often one uses the Enable input – a

typical system with several devices will naturally try to

poll each device as often as it can to maintain ‘real-

time’ control. One should keep in mind that commands

typically take about 100 msec to complete, however,

so attempting to poll a device more often than that

may not be of much benefit.

Providing an Enable input simplifies the interface

circuitry needed if controlling multiple devices, often

reducing your design to basically a channel selector,

and one ELM624 per channel. The Example

Applications section provides a sample circuit showing

one possible way of controlling three devices through

one RS232 interface.

ELM624DSD

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

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