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Bug? RSSI PWM times out with RP=0xFF

0 votes
I'm using XBee Pro DigiMesh 2.4 modules with the latest firmware (8073).

According to the documentation, if the RP register (RSSI PWM timer expiration) is set to 0xFF, this "permanently enables the pin; when configured in this way, it will always reflect the RSSI value of the last-received data packet."

However, on my modules, when the RP register is set to 0xFF, the PWM output times out after 25.5 seconds.

I assume this is a bug. Is there a workaround?
asked Feb 24, 2016 in RF Solutions and XBee by SWB01 New to the Community (0 points)
retagged Feb 26, 2016 by SWB01

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2 Answers

0 votes
The value FF is 25.5 seconds and the PWM timer still needs to expire at some point.
answered Feb 25, 2016 by mvut Veteran of the Digi Community (15,412 points)
Yes, that is what I observe. But that is contrary to the official documentation, which states that when RP=0xFF, the timer does not expire.

See, for example:

http://ftp1.digi.com/support/documentation/90000991.pdf (page 111)

http://examples.digi.com/wp-content/uploads/2012/07/XBee_ZB_ZigBee_AT_Commands.pdf (page 134)

These documents are not for that product.  They are for the XBee ZB product and not the Digi Mesh 2.4 product.  Try looking at the manual located at http://www.digi.com/support/productdetail?pid=3524.
The first link I posted (the 90000991.pdf) is the user guide for the DigiMesh 2.4.  It is, in fact, the manual located at your URL.

The other two happen to be for the ZigBee versions. The documentation for the RP register is the same in both versions.
0 votes
RP is the PWM timer expiration in 0.1 seconds. It sets the duration of PWM (pulse width modulation) signal output on the RSSI pin. The signal duty cycle is updated with each received packet and is shut off when the timer expires.

Note: When RP = 0xFF, the output is always on. This does not mean that it retains any information, just that you will get a 100% duty cycle output.
answered Feb 26, 2016 by MikeN Community Contributor (87 points)
edited Feb 26, 2016 by MikeN
Correct. But according to the documentation, the timer should not expire when RP=0xFF. However, it does. (At least on my modules with the latest firmware.) This appears to be a bug.
I just noticed your edit, "Note: When RP = 0xFF, the output is always on. This does not mean that it retains any information, just that you will get a 100% duty cycle output."

That is not consistent with either the documentation or my observations.

The documentation is very clear that with RP=0xFF, the PWM signal is supposed to continue indefinitely with the RSSI value of the last received packet.

Furthermore, on my modules with firmware 8073, the output does not remain on at 100% duty cycle after the timer expiration; the output turns off after timer expiration (0% duty cycle).