Parallax BS2px24 and AX-12
Bill Chennault
Posts: 1,198
All--
I broke down and bought two of those neat AX-12 servos. I want to control them via one of my Parallax Stamps, preferably, the BS2px24. The AX-12 seems to be a VERY intelligent servo which is controlled by an on-board eeprom. You both control and receive responses from the AX-12 via reading and writing the table.
Problem . . . maybe BIG PROBLEM for me: I bought two AX-12s (they are not here yet; 12/07/06). Although the eeprom table I mentioned has a setting for the baud rate which is configurable from 9600bps to 1,000,000bps, the factory default is 1,000,000bps at startup. The entire eeprom table is copied into an identical RAM table and most of the user's actual control and sensing takes place in RAM. The spec sheet linked to above seems very complete, but it says nothing much about that INITIAL baud rate!
Of course, my question concerns how I can make the BS2px24 communicate with the RAM table·or the default value eeprom table in the AX-12 when the maximum baud rate of the former is 19.2kbps while the initial baud rate of the AX-12 servo is 1mbps?
I wonder if I am misunderstanding something here? I wonder if my laptop's usb port will--via some usb to serial converter--let me talk to the RAM table in the AX-12 to switch its baud rate way down to something the Parallax BS2px24 will handle?
Can you help me figure this out?
Thanks!
--Bill
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You are what you write.
I broke down and bought two of those neat AX-12 servos. I want to control them via one of my Parallax Stamps, preferably, the BS2px24. The AX-12 seems to be a VERY intelligent servo which is controlled by an on-board eeprom. You both control and receive responses from the AX-12 via reading and writing the table.
Problem . . . maybe BIG PROBLEM for me: I bought two AX-12s (they are not here yet; 12/07/06). Although the eeprom table I mentioned has a setting for the baud rate which is configurable from 9600bps to 1,000,000bps, the factory default is 1,000,000bps at startup. The entire eeprom table is copied into an identical RAM table and most of the user's actual control and sensing takes place in RAM. The spec sheet linked to above seems very complete, but it says nothing much about that INITIAL baud rate!
Of course, my question concerns how I can make the BS2px24 communicate with the RAM table·or the default value eeprom table in the AX-12 when the maximum baud rate of the former is 19.2kbps while the initial baud rate of the AX-12 servo is 1mbps?
I wonder if I am misunderstanding something here? I wonder if my laptop's usb port will--via some usb to serial converter--let me talk to the RAM table in the AX-12 to switch its baud rate way down to something the Parallax BS2px24 will handle?
Can you help me figure this out?
Thanks!
--Bill
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You are what you write.
Comments
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·· I don’t see anything in the text specifying the default Baud Rate anywhere.·· I see a range and an upper limit and several times it specifies the other parameters, such as number of bits, parity, etc.· Are you sure these aren’t auto-baud?· Perhaps I missed something?
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Chris Savage
Parallax Tech Support
It is much more likely that I missed something!
Here is the quote at the bottom of page 13 from the AX-12 spec sheet that has me flumoxed concerning making a BS2px24 communicate with the AX-12 . . .
"The initial value of Baudrate is set to 1(1000000bps.)"
Here is the·link to the AX-12 spec sheet.
Thank you very much . . . again!
--Bill
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You are what you write.
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·· You are correct, and I was the one who missed that…Bummer…I wonder if it’s a typo or something.· That seems a little high for ANY Microcontroller to support by default without special code.
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Chris Savage
Parallax Tech Support
Pardon my ignorance, but is there a relatively simple half-duplex UART circuit capable of 1mbs operation that I could plug into my BOE Rev. C with the BS2px24 and start tossing bits and bytes down the wire at that neat AX-12 RAM table?
On the RoboSavvy forum a guy talks about using the AX-12 with his Propeller with no problems whatsoever. However, the Propeller is still over my head (it won't be, eventually; but I would like to start sooner rather than later).
How about one of your Bluetooth or other wireless products? (That may be extreme, but there must be a WAY.)
I got this fragment from a post on the RoboSavvy forum; perhaps it will give you an idea·concerning how to·communicate with the AX-12 with a Stamp·. . .
"I am using a PX832A (AKA Propeller) processor and it runs fine at 1Mbps.
Although the robot can be programed in Spin/ASM using this board I am currently working in a interpreter for BCP programs. I support every CM5 internal register. Now I need to interpret BCP commands. Fortunately once tokenized the commands are easy to interpret. What I want to have is a backwards compatible CM5 replacer."
I do not need 1mbs. I don't even need "fast." I just need something that will allow one of my Stamps to communicate with the AX-12 table, at any speed; 2400 baud would be fine.
Despite what the AX-12 spec sheet says, there are hints in cyberspace that the AX-12 is auto-baud. Just bare, brief hints, though.
I'll buy Parallax an AX-12 if you will develop a Stamp interface to it. Now, how can you beat a deal like that? [noparse]:)[/noparse]
--Bill
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You are what you write.
·· The USB2SER, PropPlug and PropClip all support up to 3Mbps throughput.· One of these should in theory work for you.· Take care.
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Chris Savage
Parallax Tech Support
Great! (In theory [noparse]:)[/noparse] I might not even have to buy anything since I already have the USB2SER.
I appreciate your forbearance in discussing a "foreign" product.
--Bill
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You are what you write.