Re: USB to RS232 one chip solution

"mkr5000" <mikerbgr@xxxxxxxxx> wrote in message
news:76bce20a-6403-4531-aff4-7e7ccebc81c5@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Looking at that CP2102, it looks like I can simply supply the SN75176
RS232 to the UART.

Yes... in their most generic configuration, these sorts of ICs (I'm familiar
with the ones from FTDI) really do take USB in one side and provide a (5V)
RS-232 port on the other side. The manufacturer provides the device driver so
that, as far as your operating system is concerned, you just have a new COM:
port. (Note that this implies you need a relatively modern OS with USB
support... if you have some old industrial controlling running DOS, for
instance, it's a lot iffier whether or not you'll find a driver without having
to have someone custom program it for you. But for Windows, the Mac OS,
Linux, etc., this is all easy.)

So, when I build my interface boxes I then program the chip's eeprom
via the USB port and my PC?

Yes, and strictly speaking you don't even have to program the chip's EEPROM if
you're happy with the defaults (i.e., the name of your device -- without
programming the EEPROM it'll just show up as something like, "USB to RS-232
Converter" rather than "MKR500's Cool Widget").

Just install their software and it sets the baud rate and all the
other parameters?

Yes, you set the baud rate, pairty, data/stop bits, etc. using the exact same
method you would for a "regular" RS-232 port.

At least for the FTDI chips, the newest versions of Windows (e.g., Vista) even
come with the driver pre-loaded for you when you install the OS.

The drivers are just for programming -- not needed after the chip is
burnt?

No, the drivers are always need (just as a driver is always needed for a
regular serial port in a modern OS), but the operating system takes care of
keeping them around. You use a little program (it's called "MProg" in the
case of FTDI chips) to program the EEPROM -- it communicates through the
regular operating system driver. In fact, if you want to, FTDI provides a
..DLL so that your programs can talk a bit more "directly" to the chip as well.
This gives you the advantage that you can use features that a "regular" RS-232
port doesn't provide. E.g., bit-bang the pins to load FPGA bitstreams, setup
"weird" serial modes (like I2C or SPI) that regular RS-232 ports can't, etc...
but this is all optional. Any program that knows how to talk to a regular
RS-232 port (e.g., Hyperterminal) will have no problem talking to your device.

Go poke around FTDI's web site and download some of their documentation --
this should then become somewhat clearer.

---Joel


.

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