Question about FTDI cables

[inuyasha84]

Hello guys. I have some trouble with the FTDI cables. I created a small circuit on a breadboard. I'm sure about the connections I created are good but I see something strange.

On the RTS I put a led between it and the ground. The led lights on while I connect the first time the Usb to the pc and in general the RTS is set as unasserted, while it should light on when it is asserted.

I also put a switch between CTS and the ground. In the way it is set on the breadboard it should set CTS at 1 without be pressed, in the labview debug I see that it do the opposite.

Considering that I'm sure about my circuit since I have used a tester to see if the connections and the logic was good...the question is how it is possible?is there something that am I missing?

Attached there is the circuit I created.

[Ferchu]

Hi Inu..

What are you trying to do? I can only see here from your information a little circuit and you trying to connect it using the USB port. It is not enough info to help you.

Please elaborate this.

[inuyasha84]

The circuit you see is to test a driver I have created in labview.

The idea is:

1- the user put the RTS at 1

2- when the RTS is up, a string is sent on the TXD

3- the driver does a test to see if the CTS is  on or off ( it is on when I press the switch on the circuit, off in the other case)

4- when the CTS is on, we are ready to read the response from the RXD.

it is a normal comunication protocol (or more or less normal ^^ ).

the problems are described above in my first post.

Thank you

[Ferchu]

Looking at the circuit and your explanation looks like it is something wrong on you driver app and not in the circuit.

I dont know if you have seen this web site before if not there  are some examples communicating with FTDI.

http://www.ftdichip.com/Support/SoftwareExamples/CodeExamples/LabVIEW.htm

Let me know if that help or if you are able to upload your driver so we can check it.

[inuyasha84]

Hi Ferchu.I already saw that examples.

Attached there is my driver but I don't see the error on my VI...

[Ferchu]

Mate,

This is the same as "REPORT ERROR VISA".

Shall we carry on with the other threat?

[inuyasha84]

No since the questions are different I prefer to continue to talk about this problem here. if you don't care ofc.

[RavensFan]

Actually it may be the same problem you are having in the other thread.  Your architecture may not be allowing you to detect when the signal lines are being changed.

[inuyasha84]

mmm no I don't think that is a problem of the architecture because I see that also in a simply VI without cicles or event structures the led goes on at the beginning while it should be 0.

[Ferchu]

I am sure you went through this informaiton as well.

If not double check connections.

How does RTS/CTS flow control work in an FTDI chip?

FTxxx RTS# pin is an output. It should be connected to the CTS# input pin of the device at the other end of the UART link.

If RTS# is logic 0 it is indicating the FTxxx device can accept more data on the RXD pin.

If RTS# is logic 1 it is indicating the FTxxx device cannot accept more data.

RTS# changes state when the chip buffer reaches its last 32 bytes of space to allow time for the external device to stop sending data to the FTxxx device.

FTxxx CTS# pin is an input. It should be connected to the RTS# outout pin of the device at the other end of the UART link.

If CTS# is logic 0 it is indicating the external device can accept more data, and the FTxxx will transmit on the TXD pin.

If CTS# is logic 1 it is indicating the external device cannot accept motre data. the FTxxx will stop transmitting within 0~3 characters, depending on what is in the buffer.

This potential 3 character overrun does occasionally present problems. Customers shoud be made aware the FTxxx is a USB device and not a "normal" RS232 device as seen on a PC. As such the device operates on a packet basis as opposed to a byte basis.

Word to the wise. Not only do RS232 level shifting devices (e.g. MAX232) level shift, but they also invert the signal.