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cossettej
1 Posts |
 Posted - 14 Jun 2004 : 10:50:39
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We have an embedded windows application using the GC+ in which we need to increase the priority of an interrupt for control of serial port 1. In this application it is actually a RS-232 to RS-485 converter on the GC+.
Serial port 1 is going to a RS-485 driver and one of the GPIO (GP15) is being used to control the Drive Enable (DE) line of the RS-485 chip.
Once the FIFO has transmitted all of its characters, the DE signal should be removed very quickly to allow other devices to respond and drive the bus.
The problem is that because Windows CE has not responded to the interrupt soon enough, (several milliseconds), the Drive Enable (DE) of the RS-485 driver stays on and thus drives the 485 bus for too long, causing collisions with other devices out on the bus.
Is there anything we can do to elevate the priority of the interrupt which controls the DE signal?
Or is there any other way to drive the DE signal low (False) after a byte is transmitted such as polling a bit such as TBY in the status register.
Any help is very much appreciated.
Thank you.
Kevin
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akidder
1519 Posts |
Posted - 14 Jun 2004 : 17:32:47
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Thanks for your note, Kevin. This particular item is tricky for a number of reasons, but isn't related to interrupt priority. In short, the driver has to guess when the data has been sent out the shift register, and it's typically conservative.
Give us a call or drop us a line directly and let's discuss how to best address this issue.
Cheers,
Drew |
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akidder
1519 Posts |
Posted - 19 Nov 2004 : 15:25:19
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We've recently done some work on our XScale serial drivers and have successfully reduced the time that the 485 drivers hold the bus.
If this feature is important to your production application, let us know and we can look adding these features back to older products like the GC Plus.
-Drew
p.s. I've changed the topic of your post from "Raising Interrupt Priority of GPIO for serial port" to "RS-485 holds bus too long" to clarify this topic for others. |
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