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Re: USB ->Serial(RS485) Driver

On Oct 19, 2006, at 7:51 AM, VAMSI wrote:
I have a problem developing USB -> RS485 Driver. We have a USB - Serial Device(RS232/RS485) which is implemented as a Vendor Specific Device.
We have developed a driver which uses the Class IOSerialDriverSync & IORS232SerialStreamSync which works fine when the device is in RS232 mode but does'nt work when the device is put in RS485 Mode.

The question is do i need to implement a driver based on IOSerialDriverSync & IOSerialStreamSync to work with the USB - >serial(RS485) Device or else can i make some modifications in the present driver regarding flowcontrol logic to make it work with the device put in RS485 mode.

Can anyone please suggest me on how i can make my driver work with the USB->Serial(RS485) Device.

RS232 is full-duplex (independent Tx and Rx lines) and is used for point-to-point connections. RS485 commonly uses a shared data line and multi-drop topologies. To support this, there must be a mechanism at the driver level to gate the transmitter for each node, and a protocol to select which node can transmit at any given time.

The IOSerialDriverSync & related classes assume a full-duplex point- to-point communication channel, and don't have any built-in capabilities regarding line turnaround. You should in theory be able to implement this control protocol in your driver, such that the superclasses don't need to know or care about the line control (when it isn't your turn to talk, act as if you are flow-controlled off).

If your RS485 link is wired as a full-duplex point-to-point link, then your driver should probably work as-is, unless you need something extra to enable the transmitters.

Hope this helps,
 - Dean


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 >USB ->Serial(RS485) Driver (From: "VAMSI" <email@hidden>)



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