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RE: [Paparazzi-devel] Soft uart possible?

From: mark.griffin
Subject: RE: [Paparazzi-devel] Soft uart possible?
Date: Mon, 14 Sep 2009 11:26:38 +0200

Hi Timo,

Yes, both hardware UART ports are used on the LPC2148 (for GPS and
The only option for a third UART is via software. 

I understand that the LPC2148 is 40-60% utilised when running the
paparazzi code so there is some remaining capacity available. For low
serial speeds, polling a pin would be sufficient. However for high
speeds, timers & interrupts would be necessary.

The timer and interrupts associated with the PPM input (pin#30/CAP0.2)
could be used for software serial input instead. I haven't tried it and
not sure if anyone else has.

The open-source mikrokopter project has some c code to decode the 115200
bit/s serial signal from a 2.4 GHz Spektrum satellite receiver at:
&path=%2Ftags%2FV0.74d%2FSpectrum.c Although based on the ATMega644P
using a hardware UART, it could be adapted and implemented in the
Paparazzi system. I haven't tried it and not sure if anyone else has. It
seems feasible.

The alternative is to use the PPM encoder board
( The
Spektrum serial signal could be input on the "servo 1" pin (pin#30/RXD)
which can be configured as hardware serial input. The code could then
decode the signal and output PPM to the autopilot.

Hope this helps.

Cheers, Mark 

-----Original Message-----
From: address@hidden
[mailto:address@hidden On
Behalf Of Timo Drick
Sent: mercredi, 2. septembre 2009 01:31
To: address@hidden
Subject: [Paparazzi-devel] Soft uart possible?

Hi all,

it would be nice to have some more uart ports at the Twog or Tiny v2. 
Did anyone try to implement a soft uart.
One application would be to read 2.4 Ghz Spektrum receiver data. The
satalite receiver send serial data with 115 kBaud data rate. Only a RX
uart pin is needed to read the receiver data. If this works no ppm
encoder board and only 3 wires are needed.

regards Timo

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