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Forum Index : Microcontroller and PC projects : Serial Support of RS-485

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CircuitGizmos

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Joined: 08/09/2011
Location: United States
Posts: 1425

Posted: 08:04pm 26 Sep 2011

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Do the serial routines support the driver-enable that is necessary for interfacing to an RS485 driver chip?

In other words a "driver enable" line that is active at the beginning of the byte transmission and remains active until the conclusion of the stop bit of the transmitted byte?

(Or related to this, is the call to send a serial character a "blocking call" that waits to return until the last bit is sent?)

I'm guessing that with the buffering of serial communications, there is not yet support for correctly implementing the driver enable.

Micromites and Maximites! - Beginning Maximite

haiqu

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Joined: 30/07/2011
Location: Australia
Posts: 152

Posted: 12:33am 27 Sep 2011

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RS232 to RS485

unzip, strip, touch, finger, grep, mount, fsck, more, yes, fsck, fsck, fsck, umount, sleep

CircuitGizmos

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Posted: 12:40am 27 Sep 2011

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haiqu said RS232 to RS485

I have plenty of those. I know just how they work. That isn't what I'm asking for.

Micromites and Maximites! - Beginning Maximite

Geoffg

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Joined: 06/06/2011
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Posted: 12:47am 27 Sep 2011

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No, there is no "driver enable" line. Also, the routines that send a character do not block, they return immediately.

However, perhaps you could get the same effect with:

100 PIN(xx) = 0 ' enable active low
110 PRINT #1, character$; ' send a single char on the port opened as #1
120 PAUSE 1 ' wait for the char to flush at 9600 baud
130 PIN(xx) = 1

Not very elegant but it might work

Geoff

Geoff Graham - http://geoffg.net

CircuitGizmos

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Posted: 01:17am 27 Sep 2011

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Geoffg said No, there is no "driver enable" line. Also, the routines that send a character do not block, they return immediately.

However, perhaps you could get the same effect with:

100 PIN(xx) = 0 ' enable active low
110 PRINT #1, character$; ' send a single char on the port opened as #1
120 PAUSE 1 ' wait for the char to flush at 9600 baud
130 PIN(xx) = 1

Not very elegant but it might work

Geoff

With all due respect: Ick. I've done that with poor results interfacing with equipment.

I hate to have to dig into code and chip function to shoehorn something like this in.

Micromites and Maximites! - Beginning Maximite

Xiongmao

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Joined: 25/08/2011
Location: Australia
Posts: 48

Posted: 09:31am 27 Sep 2011

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The usual way (for PC ports, at least) is to drive the TXen line with the RTS signal.
However; not all PIC32 uart ports have an RTS wired out. Also, while its better, it's really only a slightly more sophisticated way of 'bit-banging' the enable line anyway.

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