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Forum: RDM Timing Discussion May 26th, 2015
Replies: 10
Views: 8,489
Posted By Nigel Worsley
Looks like a very good reason not to use a...

Looks like a very good reason not to use a timeout to detect end of packet! However if this is unavoidable then the specification can still be met:

Set the timeout to 1.05mS
When a timout is...
Forum: RDM General Implementation Discussion January 15th, 2015
Replies: 1
Views: 4,239
Posted By Nigel Worsley
There is a typo in the draft, on page 94 the text...

There is a typo in the draft, on page 94 the text DISCOVERY_INCREMENTAL is rendered in the Windings font and shows as symbols. Somewhat appropriately, the final one is a sad face :)
Forum: RDM General Implementation Discussion March 3rd, 2012
Replies: 6
Views: 7,613
Posted By Nigel Worsley
The exact amount of time will be dependent on the...

The exact amount of time will be dependent on the design of the UART, but should be fairly consistent. If using a typical 16x baud rate clock the variability would be +/- 0.125uS which is totally...
Forum: RDM Physical Layer/Hardware Discussion June 12th, 2009
Replies: 24
Views: 17,555
Posted By Nigel Worsley
I stand ( well, sit actually... ) corrected! ...

I stand ( well, sit actually... ) corrected!

I don't have a copy of the RDM spec to hand, I was intending to check that figure this evening. This means that the UART will need to be run at 50kbps...
Forum: RDM Physical Layer/Hardware Discussion June 12th, 2009
Replies: 24
Views: 17,555
Posted By Nigel Worsley
The easiest way is not to bother! Tie the...

The easiest way is not to bother!

Tie the RS485 driver chip's Driver Enable signal to the Not Receive Enable and the UART will never see the transmit data in the first place.
Forum: RDM Physical Layer/Hardware Discussion June 12th, 2009
Replies: 24
Views: 17,555
Posted By Nigel Worsley
For receiving, a framing error with data of 00H...

For receiving, a framing error with data of 00H can be assumed to be a break.

For transmitting, then assuming that the UART doesn't support sending of breaks then either of the following should...
Forum: RDM Timing Discussion May 23rd, 2009
Replies: 6
Views: 12,674
Posted By Nigel Worsley
Having used several different manufacturer's...

Having used several different manufacturer's offerings ( but not for DMX ), I am pretty sure that you are still correct. These all needed custom drivers, which caused no end of problems, so I now use...
Forum: RDM Physical Layer/Hardware Discussion August 5th, 2008
Replies: 7
Views: 8,213
Posted By Nigel Worsley
A capacitor after the diode will sort out the...

A capacitor after the diode will sort out the impedance issue, it doesn't need to be particularly large as the impedance is only relevant for higher frequencies - 100nF would probably be enough. Add...
Forum: RDM Physical Layer/Hardware Discussion December 5th, 2006
Replies: 3
Views: 8,063
Posted By Nigel Worsley
Th equations are: Vbias = Vcc * 1 / ( 1 /...

Th equations are:

Vbias = Vcc * 1 / ( 1 / Rt1 + 1 / Rt2 ) / ( 1 / ( 1 / Rt1 + 1 / Rt2 ) + R1 + R2 )

Rterm = 1 / ( 1 / Rt1 + 1 / ( R1 + R2 ) )

The specification requires Vbias to be...
Forum: RDM Physical Layer/Hardware Discussion November 30th, 2006
Replies: 3
Views: 8,063
Posted By Nigel Worsley
Change Rt1 to 150R and R1, R2 to 390R. This...

Change Rt1 to 150R and R1, R2 to 390R.

This gives almost exactly the same bias voltage, and is reasonably close to the 120R impedance requirement ( 126R ). Using difficult to obtain ( in small...
Forum: RDM Interpretation Questions October 17th, 2006
Replies: 4
Views: 6,329
Posted By Nigel Worsley
As Scott has already mentioned in a separate...

As Scott has already mentioned in a separate thread, sub-devices where intended for dimmers, where each sub-device is identical ( or at least very similar, eg. non-dim or 2.5K/5K channels ). Where...
Forum: RDM General Implementation Discussion September 24th, 2006
Replies: 3
Views: 6,416
Posted By Nigel Worsley
You are forgetting two things: The SN75176...

You are forgetting two things:

The SN75176 is a very old device, and more modern transceivers usually guarantee that a 0V input will give a high output. The MAX485 datasheet says: "The receiver...
Forum: RDM Interpretation Questions July 3rd, 2006
Replies: 1
Views: 5,112
Posted By Nigel Worsley
Question Error counters

10.2.1 says 'Short Message - The message ended before the Message Length field was received', and the other two error counters only count messages with a matching UID. What should happen if a message...
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