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connecting tx/rx to an rs232>usb converter

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dequo:
I have an angle sensing instrument that communicates with rs232 protocol to a com port on the computer via http://australia.rs-online.com/web/p/products/0550170/ , i am trying to read it on the com port but im not getting anything at all.
the device has 4 wires - power, ground, RX, TX

the TX from the device is connected to the RX in the DB9 RS232 connector (pin 2)
RX connected to TX (pin 3)
Ground connected to ground (pin 5), also connected to power supply ground
power connected to power supply ground

i have set the specified port options in the device configuration (115200 baus, start bit 1, stop bit 1, data bit 8,no parity checks, no flow control)

anything im doing obviously wrong? do i need to do something with all the DB9 pins other than TX, RX and GND?

IanB:

--- Quote from: dequo on October 05, 2011, 07:38:00 am ---anything im doing obviously wrong? do i need to do something with all the DB9 pins other than TX, RX and GND?
--- End quote ---
It's possible. You need to the exact specs and connection requirements of the device you are communicating with. Sometimes it might be required to connect other signals like DTR to enable communication. If in doubt you should use a fully wired cable with all pins connected. You might also check voltages. I think "officially" you need 12 V signals for RS-232, though a lot of hardware is forgiving in this respect.

Bored@Work:
Did you really pay 60 AUD for that adapter? Because that is 10x more than normal.

And are you sure that you really have an instrument using RS232 voltage levels, as opposite to 5 V or 3.3 V logic levels? The power wire is rather suspicious, because it is uncommon (i.e. non existing) on real RS232 interfaces.

desowin:

--- Quote from: dequo on October 05, 2011, 07:38:00 am ---the device has 4 wires - power, ground, RX, TX

--- End quote ---

What is this device?
Looks like it's just plain UART on TTL levels, not RS232 levels (positive or negative voltages in range 3-15V). For that you'd need (assuming you want to connect to USB on computer side) something like Microchip MCP2200 or FTDI FT232.


--- Quote from: dequo on October 05, 2011, 07:38:00 am ---anything im doing obviously wrong? do i need to do something with all the DB9 pins other than TX, RX and GND?

--- End quote ---

Well, if target device operates on TTL levels, then it's likely that you are close to (or already did it) frying it.

dequo:
ok, either its labelled wrong or im an idiot. connecting what is apparently TX on one to the TX of the other works...

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