Problem setting up UART cable

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Anonymous
Not applicable

 Hi,

I'm trying to use an FTDI TTL-RS232-3v3 cable with a PSoC1 chip - CY8C27443.

I'm having trouble defining the input and output pins for the cable. My board is set to be powered externally and regulated at 3.3V (using the Eval1 board). The cable says it is rated at 3.3V for all the signals (RTS/CTS/Tx/Rx). There is an extra pin on there for 5V output from the cable (coming from USB), I have left that disconnected.

I have set RTS and Tx (which are the board's CTS and Rx respectively) to be HIgh Z pins. However, it seems as though when these pins are both connected to port 2, the board is being powered. When the cable is connected, measuring the board's Vcc to GND gives ~1.78V. The pins on the cable read ~2.57V (between either two of the input pins and ground).

Why is this happening? Do I have to set up some BJTs or something and, instead, pull the cable's input pins to its ground pin (externally from the board)? I'm really confused..

   

 

   

Thanks,
Matt

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Anonymous
Not applicable

 Oops, I meant, do I have to set up BJTs and pull a pin to Vcc if the cable's input (input to my board, output from the cable) is 3.3V.. Output pins would be the other way

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ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

The 2.57 is suspicious, ~ a diode drop below 3.3. The Eval1 regulator has a 2 V dropout

   

voltage, are you feeding it > 5.3 V ?

   

 

   

Regards, Dana.

   

 

   

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Anonymous
Not applicable

 Ah, using a 9V to power the board. I assumed that the regulator would wrk with it.

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ETRO_SSN583
Level 9
Level 9
250 likes received 100 sign-ins 5 likes given

Consider posting the project and a schematic for the forum to look at.

   

 

   

    

   

          

   

"File"

   

“Archive Project”

   

Use Internet Explorer or Firefox to post, Chrome does not seem to work.

   

 

   

Regards, Dana.

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