RS Media Robot serial hack

[freddya]

My goal is to make a wireless serial connection to the robot as if it were wired to my laptop.
I have 2 xb24 version 1084, usb explorer, explorer regulated.
The Robot has rx, tx, gnd and 3.3v pads.
As I understand it would be a AT transparent setup.

1. Phisical connection to Explorer Regulated from robot, DOUT = RX, DIN = TX, GND = GND. is this correct?

2. What about power? Can I connect the robot 3.3v to the explorer 5v (at the edge of the board) or should I connect directly to the 3.3v on the explorer (looks like direct to the 3.3v xbee pin) instead?

3. USB explorer on x-ctu on my laptop says USB Serial port (com4) so it looks like at least that module is connected. After soldering the explorer regulated to the robot pads, how do I connect to it?

4. I’ve read about firmware upgrade, is that needed for AT to proceed?

5. What next to make this serial connection happen?

[freddya]

Ok I’ll take the time to respond to my own post.
1)correct physical connections
2)3.3v to the explorer 5v works, also to the 3.3v pin1 on xbee.
3)connect the radios by configuring sh/sl on dh/dl on both radios.
4)Firmware 1083 was from factory, garbled communications 9600 through 115200, Updated to 10CD same results, cannot downgrade to any firmware now to test others, connection to modem lost. Tried the 2 stop bits on the hyperterminal no fix.

So it looks like my serial hack is almost complete, just need to fix the sloppy connections.

1st xbee on usb explorer.
2nd xbee on robot. voltage to pin 1 = 3.3v, tx, rx, and gnd are all that I have connected.

here is what I get on hyperterminal as far as the sloppy connection goes

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Any solution for this problem? Thanks

[johnf]

> 3.3v to the explorer 5v works, also to the 3.3v pin1 on xbee.

I’m not sure what you mean by this, but I hope it doesn’t mean you’re actually feeding 5V to the XBee. That would be a sure recipe for disaster…

> cannot downgrade to any firmware now to test others, connection to modem lost.

There are a few suggestions in the FAQ for dealing with the situation where X-CTU can’t talk to the XBee. Version 10CD should be fine though (although it isn’t the latest).

Reading between the garbled bits in the terminal printout, the far send seems to be reporting quite a few error messages - so something’s apparently wrong there.

Also, I’m guessing that the output is being generated at a fairly high rate. Given that, you’re probably going to need to implement flow control on the connection in order not to lose characters. However, lack of flow control shouldn’t lead to garbled characters.

What was the baud rate you were using when you captured the output?

[freddya]

Hello Johnf, thanks for taking a look here. The RS Media only puts out 3.3v so what I meant was that I could connect the 3.3v to the 5v input of the explorer regulated with the xbee on it and it would power up normally. I read up on the xbee power input before anything.
As fas as the x-ctu, it does read both xbee’s at 115200, and I can do At configs, just cant do any firmware updates after updating to 10CD. So i’ve stayed on 10CD. The robot communicates at 115200 and I have configured both xbee’s at that speed and have set 2 stop bits on the hyperterminal with no improvement. So the captured output was using 115200.
Freddy

[freddya]

Hello Johnf, thanks for taking a look here. The RS Media only puts out 3.3v so what I meant was that I could connect the 3.3v to the 5v input of the explorer regulated with the xbee on it and it would power up normally. I read up on the xbee power input before anything.
As fas as the x-ctu, it does read both xbee’s at 115200, and I can do At configs, just cant do any firmware updates after updating to 10CD. So i’ve stayed on 10CD. The robot communicates at 115200 and I have configured both xbee’s at that speed and have set 2 stop bits on the hyperterminal with no improvement. So the captured output was using 115200.
Freddy

[johnf]

Ok. Thanks for the reassurance on the power!

I tried googling for technical details on the robot but didn’t come up with very much, except for one mention that its processor has a system clock of 200 MHz. That rang some alarm bells.

Now, I’m going to make a couple of assumptions here and then stick my neck out with a theory. The theory might still be broadly right even if the assumptions are wrong, but its case would be weakened.

Assumption: the scenario you’re describing is that an XBee is mounted on the robot, communicating with the second XBee attached to a PC.

Assumption: you’ve found a way to tap in to a direct RS-232 connection on the robot (my googling suggested that the robot output was via USB).

Observation: your hyperterminal capture does look very much like a baud rate mismatch. In fact, when characters are corrupted over a serial link there’s very little other than extreme noise that can explain it.

You say you tried two stop bits in hyperterminal but that it made little difference. At 115200 baud, two stop bits at the PC end do make sense, so keep them in and keep reading.

It’s the serial link between the robot and its XBee that I now think may be causing the problem. If the robot system clock is 200 MHz, and if it uses the standard algorithm (that’s two more assumptions…), it’ll divide that clock by (16 * x) to get the baud rate, where x is the nearest integer to the theoretically correct value. The theoretically correct value for x is 200M / 16 / 115200 = 108.506, so the nearest integer is 109.

The robot’s actual baud rate is therefore presumably 200M / 16 / 109 = 114,678.89 baud.

However, the best the XBee with its 20 MHz clock can manage is 111,111.11 baud. The difference between these rates is 3.2% and that’s rather a large difference.

So I think you may need to look at the robot-XBee link and adjust something. There are two possibilities: either set the robot to send two stop bits, or set the robot to use a custom baud rate as close as possible to 111,111.11 baud.

To choose between the two possibilities: I would set two stop bits on the robot. If you change the robot’s baud rate, you’ll then re-encounter the original problem when you connect the robot directly to a PC.

[freddya]

Johnf, Your are correct in the setup you described and there is a serial connection available on the media board of the robot where I have soldered the radio. So I am currently attempting (with the help from Helibot, a well known user at robocommunity.com) to set 2 stop bits or a diffrent baud rate on the robot, even to a 57600 rate that might be more reliable? I will post any updates ASAP thanks again for your in depth help on this. Almost there!

Freddy

[freddya]

OK, Success! But not at 111,111.11 since the program used does not support custom rates. I will hope to be able to use 115200 by some custom program running at the robot end or somehow setting 2 stop bits more favorably. 57600 is good for now I’ll be testing some ppp. Thanks for your help Johnf