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ELM624 Datasheet(PDF) 11 Page - ELM Electronics |
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ELM624 Datasheet(HTML) 11 Page - ELM Electronics |
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11 / 16 page  looked something like these: 0 6 1 2 2 4 5 8 0 6 3 2 4 9 1 1 0 6 4 2 0 1 0 0 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. 11 of 16 ELM624 ELM624DSD Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > 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. Talking to Your LANC Device (cont’d) |
Similar Part No. - ELM624_1 |
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Similar Description - ELM624_1 |
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