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[DPRG] Serial Woes

Subject: [DPRG] Serial Woes
From: Eric Sumner kd5bjo at gmail.com
Date: Sat Feb 3 13:54:27 CST 2007

> I noticed on my Acroname serial biscuits (BrainStem modules) that I have a
> jumper soldered from pin 7 to 8 (CTS RTS). Don't know if that has anything
> to do with your problem. I think that was to satisfy Air Cable since I think
> on PC I am not using handshaking. In fact, when I use hyper terminal, I tell
> it no hand shaking.

The problem appears to be on the TTL side, as I can successfully do a
loopback test through the Acroname module.

> Are you sure what data polarity is expected on Parallax end? The BrainStem
> inverts data of course having a Max232 or somesuch inverting driver/receiver
> chip on it.

The outgoing path appears correct (direct connection), as the servo
controller changes its outputs correctly; the problem is that the
servo controller is crashing whenever the Acroname RX is connected
seemingly at all.

> You will need to invert it again possibly if Parallax module is expecting
> RS-232 polarity on signals, but just tolerant of higher voltages and hoping
> your RS-232 receiver is happy with 0 to 5 volt swings on its transmitted
> data.
> Look at the device's TX level when it is not sending. Is it high or low?

One pertinent detail that I apparently left out of my original post:
The Parallax board has only one serial line that it uses for both TX
and RX, and I don't know exactly how they're doing it.  The processor
can set its pins to any of 5 different states (High, Low, High-Z,
Pull-up, or Pull-down), and I can't really tell which mode it's in at
any given time.

  -- Eric

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