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Forum Index : Microcontroller and PC projects : CP2102 TTL-USB Bridge
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crackerjack Senior Member  Joined: 11/07/2011 Location: AustraliaPosts: 164 |
Hi, I recently picked up a couple of USB-UART (TTL level) boards based on the SilLabs CP2102 to interface the Maximite back to a PC via the Serial comm's functions, e.g. Open "Com2:9600" AS #1 Print #1, 0 Close #1 I am fairly sure I have the hardware connected right: Maximite Bridge +------- -----+ | GND <-----> GND | | PIN 19 <-----> TXD | | PIN 20 <-----> RXD | +------- -----+ ...and I have TeraTerm open on the COM port my Device Manager says is the Silicon Labs CP210x USB to UART port (COM8) with the Serial port settings as Baud Rate=9600, Data=8 bit, No Parity, 1 Stop bit, No flow control. I don't have a 'scope with me at present, so I'm guessing somewhat and I can't get any comm's happening. I've also tried using COM1: from the MM (pins 15 as RX and 16 as TX, crossed over to the Bridge device) - no luck. I even tried crossing the pins over to what seems like the wrong way (RX - RX, TX - TX) - mostly because I am desperate... Any tips, experience, or insights offered will be most graciously received... Cheers, CrackerJack. |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
Ignore the Maximite for the minute and plug the cable into the pc on its own. Short out the tx and rx pins on the loose end and see if you can talk to yourself with your terminal software. Once you now that works, then take the short off and connect it to the Maximite, then we can go from there. Cheers Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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| JohnS Guru  Joined: 18/11/2011 Location: United KingdomPosts: 3800 |
^ what he said. A loopback cable is a good idea when stuck like this. BTW, you might (read: do) want to be a bit careful about the voltage levels.... John |
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| crackerjack Senior Member Joined: 11/07/2011 Location: AustraliaPosts: 164 |
Thanks for the responses. I tested as Rohan suggested and all is good - loopback is working (local echo off on the terminal and I see what I type coming back). I had literally 3 minutes to test this. More when I get another three minutes.... |
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| crackerjack Senior Member Joined: 11/07/2011 Location: AustraliaPosts: 164 |
Ok, I know this may not help anybody else, but for the sake of completeness, the problem is solved. As per Rohan's suggestion, I looped-back on the USB-UART bridge - all worked as it should. I tried connecting the Maximite again - still no luck. Got my oscilloscope out just to trace the waveform on the output from the Maximite - all seemed fine. Put the 'scope onto the pin marked TXD of the USB-UART while entering data from the keyboard with TeraTerm. No signal. Put it on the RXD pin and hey, there was the signal... So, it seems the pin marked RXD goes to the pin on the device Receiving. from the USB and the pin marked TXD goes to the pin on the device Transmitting from the USB. Counter-intuitive? Maybe, maybe-not - anyway... all fixed. The USB-UART bridges were bought from ebay for a very small sum. They are cheap, but nifty little items in this day and age when a serial port on a PC is just not to be found. Thanks again for the useful input Rohan and John. Cheers, Lance. |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
Glad you got it working. Your device sounds like it conforms to one of the 75000 versions of the rs232 standard. 
Cheers Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3800 |
It may go back to the old "is it DCE or DTE" thing. Best ignored, especially once it's working!! So many times I've wished every device was peer-to-peer without exception (and each end symmetrical, so no DCE/DTE issues, no master/slave, etc). John |
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