Are RxD and TxD swapped on ATZB-900-B0?

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billysugger
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Posted by billysugger: Thu. Jan 5, 2012 - 09:23 AM
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I'm developing with the ATZB-900-B0 and SerialNet, and am having problems with serial interfacing. The datasheet (8227C-MCU Wireless-06/09) insists that the module transmits with TxD (output) on pin 13 and receives with RxD (input) on pin 14. But the modules I have stubbornly transmit on pin 14 and receive on pin 13.

Of course my assumption has been that I have mis-read the datasheet, mis-interpreted the signal directions or something else, but everything I try seems to confirm that the datasheet is wrong. This seems so unlikely to me, especially as I can find no reference to such a problem on Google.

Before I re-spin my board, can anyone else confirm whether the datasheet is correct, or whether I have to swap these signals?

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

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Wireless, General Wireless Discussions
Last Edited: Fri. Oct 16, 2015 - 02:25 PM
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billysugger
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Posted by billysugger: Thu. Jan 5, 2012 - 01:32 PM
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Found it! There is a small-print note on P3-7 which says:

Quote:
The UART_TXD pin is intended for input (i.e. its designation as "TXD" implies some complex system
containing ZigBit 900 as its RF terminal unit), while UART_RXD pin, vice versa, is for output.

This is in direct contradiction with the entry for the pin in Table 3-6 which declares the pin as an output.

Conversely, on the datasheet for the ATZB-24-B0 the same UART_TXD pin is declared as an input.

Watch out for this nasty feature!

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

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floresta1212
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Posted by floresta1212: Thu. Jan 5, 2012 - 02:28 PM
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Quote:
Watch out for this nasty feature!
Anyone who has used the RS-232 'standard' for any length of time has probably run into this feature at one time or another.

The person who determined the pin connections for this device intended it to be used in a DCE (Data Communication Equipment) device such as a modem. The person who wrote the 'Description' in the data sheet was not aware that in such a device the TxD pin is an input and the RxD pin is an output. The person who wrote the footnote was semi-aware of this distinction but shouldn't have characterized a DTE <--> DCE connection as a "complex system".

The purpose of this seemingly deceptive labeling is to permit the use of a 1:1 (non inverted) cable when connecting a DCE device such as a modem to a DTE (Data Terminal Equipment) device such as a dumb terminal or a computer.

Don

[Edit] Check this out:
http://www.bb-elec.com/bb-elec/l...

[Re-edit] They have changed the location, here is where it is now:http://www.bb-elec.com/Learning-Center/All-White-Papers/White-Papers-Category1/FAQ-RS-232-Connections-That-Work.aspx

Otherwise search for "RS-232 CONNECTIONS THAT WORK!"

Last Edited: Thu. Jun 6, 2013 - 01:01 PM
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billysugger
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Posted by billysugger: Wed. Jun 5, 2013 - 02:57 PM
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Indeed, I have run into this plenty of times at equipment level, but never at silicon level. And that doesn't excuse one part of a datasheet declaring a pin as an input while another part of the same document declares it as an output, and with the least obvious reference being the correct one.

After all this time, it still makes me go Grrrrrr!!!

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

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alexru
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Posted by alexru: Wed. Jun 5, 2013 - 03:55 PM
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billysugger wrote:
Indeed, I have run into this plenty of times at equipment level, but never at silicon level.
It is not at a silicon level, ATmega1281 inside ZigBit module has correct pin assignment, but then pins are swapped on the module level to make this module appear as a modem device. Not that I like it a lot, but it makes sense.

NOTE: I no longer actively read this forum. Please ask your question on www.eevblog.com/forum if you want my answer.

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billysugger
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Posted by billysugger: Wed. Jun 5, 2013 - 11:15 PM
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Oh I don't mind which way it's pinned, so long as the datasheet's clear and consistent, which this is not (or was not, if by chance it's been corrected).

Electronic components work on the principle of smoke; I know this because when I let the smoke out, they stop working. Also, sanity is over-rated.

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