Replies

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  Posted by diablero at Sat Dec 10, 2011 9:10 am

  For the first question (pin names followed by a hash) the answer is simple: the pins are all active low (the others, not followed by a hash are active high). For the second question, I worked with FTDI232H one year ago and I used only a 5V regulator on mmy board. As I remember, you can obtain a 3V3 voltage form one pin of the chip (if necessary for you). Let me find my scheme and I hope I'll answer all your questions. I'll see your schematic to see what you have done.

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  Posted by Neil Rush at Sun Dec 11, 2011 6:47 am

  Thanks for the answers everyone!

   

  Diablero: Thanks for the explanation on the hash marks, that's what I thought. I want to use the 3V3 output to power the GPS (the GPS uses 3V, but I have been informed that 3V3 won't 'hurt' it) and I dont want to put too much strain on the 3V3 output of the FT232H, although, I was thinking, perhaps it would be better to just power the GPS using it's batteries, I'd be quite happy too, and I suppose that it would work, If I just left the power supply input to the GPS disconnected.

  Michael: Thanks for the tip, I'll have a look and see what there is. The place I got information on the Garmin connector also sold cables that go from the garmin plug to bare wires, perhaps I could connect one to the cable you mentioned.

  My main objective is to design and build a cable to connect the serial port on a Garmin eTrex GPS receiver to the USB port on a computer, but I'm not too good (well, ok, I'm VERY BAD) at soldering, so perhaps I could settle on just joining the FT232H cable to the Garmin cable. The reason for wanting to design this is that Garmin charge WAY too much for their cable (over US$30), and then, if, like me, you're using a new computer that doesn't have serial ports, you have to purchase a serial-USB adapter, which Garmin sell (again, at around US$30), or from another manufacturer (as low as US$10). All in all, you're looking at easily over US$40, so I thought It would be useful to design a single-cable solution with a bridge chip, that would cost less to make than the Garmin cables cost to buy.

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  Posted by banjohat at Sun Dec 11, 2011 8:54 am

  Wow, lot of questions there :)

  I will try to answer some of them as well:

  1) On the datasheet for the FT232H, some pin names are followed by a hash (#), such as RESET#. What does that hash stand for?

  As said, that is active low signals.

   

  2) Their are several 3V3 inputs. One must be connected to the USB 5V through a 3V3 regulator, and I was wondering if I could connect the others in the same way? Also, would I need separate regulators, or could I use just one, I realise the implications caused by power usage, I can work out those for myself, but is there anything else I should bear in mind?

  If I remember correctly, the 3V3 is an output that can be used to supply a little current for a MCU. You just need 5V and then you're good to go. however, the 3V3 cannot! power the GPS. Go for a linear regulator (search for it on RS) to power that from the USB bus.

  3) As I mentioned above, RESET is active low, and so a voltage must be present at that pin. Should I use the 5V directly from USB (one of the power inputs on the FT232H is 5V), or should I use the 3V3? If I use 3V3, where should it come from? Should I use a resistor to connect the pin, and if so, what value should I use?

  Tie it to 5V

  4) The datasheet does not mention what frequency oscillator should be used. What frequency oscillator should be used?

  Without reading that much into this, the OSC is internal by default. You have the OPTION to put on your own but it is not necessary.

  5) The FT232H is a single channel hi-speed USB to multipurpose UART/FIFO bridge. It bridges between USB and one of several UART/FIFO interfaces, the default of which is RS232. I want to use RS232, so I shouldn't need to configure it. All I want is a bridge, I don't need anything fancy, so will I need to attach an EEPROM (the FT232H has provision for this, and I know how), and if so, what should be written to the EEPROM?

   

  It sounds to me that you would much rather like to use the FT232RL - which comes in a easier packaging. The sparkfun library already has the part so no need to design one yourself.

  datasheet: http://pdf1.alldatasheet.com/datasheet-pdf/view/144591/FTDI/FT232RL.html

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  Posted by Neil Rush at Tue Dec 13, 2011 9:58 am

  Thanks for the tip about the FT232RL. I'll definatly use that instead. Still grateful to all those who gave advice on the FT232H.

  The FT232R is way easier to understand and I've almost finished the circuit, aside from a little confusion about the level converter, as you can see in my edited question above.

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  Posted by Neil Rush at Tue Dec 13, 2011 10:00 am

  I've updated this question to reflect the current status of my project. Some answers may not seem to make sense, and this is why.

  I'm currently working on a design for a project to connect the RS232 port on a Garmin eTrex GPS receiver to the USB port on a computer. I've settled on using the FTDI FT232R as the bridge between the RS232 and USB ports. I've currently got pinouts for the Garmin RS232 port (as it uses a proprietary plug, not a DB-9) and a USB port, and I've also located a datasheet for the FT232R. The FT232R datasheet has application examples which told me basically all the wiring that I need to do, but when it comes to connecting the RS232 pins, I became confused:

  According to the datasheet, the RS232 pins on the FT232R should be connected to a RS232 level converter. After researching what this was, I discovered that it is an IC used to convert the voltages provided by an IC (0 - +5) to those used for RS232 communication (-14 - +14), however, the GPS in question only uses 3V, so do I still use this converter, or do I use one with differant voltages (-3 - +3v?)?

  I've attached my circuit diagram so far in GIF. It shows the circuit based on the application example from FTDI with the level converter.

  The CBUS pins have the following assignments:

  CBUS0: TXLED

  CBUS1: RXLED

  CBUS2: GPIO2

  CBUS3: GPIO3

  CBUS4: SLEEP#

  I've also attached the datasheet for the FT232R in PDF.

• 

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