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Author Topic: Guruplug Server Plus built-in serial port?  (Read 2799 times)
caseih
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« on: April 28, 2010, 02:19:59 PM »

I know the guruplug server plus does not have a built-in USB to serial adapter.  But it appears that there is a connector labeled uart RS232.  Is that a real serial port?  Can I connect with a normal null-modem cable to that and get a serial console?  Looks like a normal 4-wire serial interface to me, from the pictures.
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daemondust
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« Reply #1 on: April 28, 2010, 03:40:56 PM »

Kind of.  Yes, it has an asynchronous serial port available.  No, it isn't at standard RS232 voltages.

RS232 uses +- 3-15v signaling, while this uses 0-3v signaling.

You will need something to convert the voltages if you want to use it with RS232 compatible devices.
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superpat
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« Reply #2 on: April 29, 2010, 02:24:55 AM »

@daemondust

Hi,

I just had a look at the schematics for the Guru,  the only  serial I can find is connector J7, a four pin connector with RXD on pin 2 and TXD on pin 3, but no control signals.

I must have missed the async serial port, please can you tell me what is the connector designation, and what sheet of the schematics I can find it on?.

I could use a serial port in my project!

Many thanks

Patrick
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daemondust
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« Reply #3 on: April 29, 2010, 05:34:41 AM »

That header has 3.3v, ground, data in and out.  It doesn't have any other signaling pins.  If you want flow control I believe you can pull them off the unpopulated U15 pads if you change some pin configuration.  Pins 5 and 6 of that look like they're configured to be I2C SDA and SCK, but since they go back to MPP[8] and MPP[9] they can be reconfigured as RTS and CTS.  However, that would require opening the plug and soldering wires to it.

MPP[15] and MPP[16] can also be configured to be RTS and CTS, but those are being used as bits 2 and 3 of the microSD card data pins.

The table that has what pins can do what is on page 53 of the processor's hardware manual.
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caseih
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« Reply #4 on: April 29, 2010, 12:01:07 PM »

Kind of.  Yes, it has an asynchronous serial port available.  No, it isn't at standard RS232 voltages.

RS232 uses +- 3-15v signaling, while this uses 0-3v signaling.

You will need something to convert the voltages if you want to use it with RS232 compatible devices.
Okay.  While I could probably come up with a chip to convert it, for now I'm just going to order the jtag device.  It's too bad they don't have it built in like they did on the sheevaplug.
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daemondust
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« Reply #5 on: April 29, 2010, 12:23:28 PM »

Actually, for a lot of purposes this is better.  You can interface with anything that speaks async. serial with just a voltage difference instead of only being able to interface with USB masters.
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MarkF
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« Reply #6 on: April 30, 2010, 06:36:39 AM »

If you are adding the JTag device to allow an application to use the RS232 port (not for debugging purposes), you could use a USB-2-Serial converter in the standard USB port instead.  It might be cheaper/easier. Smiley
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Mark

daemondust
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« Reply #7 on: April 30, 2010, 07:20:11 AM »

If you are adding the JTag device to allow an application to use the RS232 port (not for debugging purposes), you could use a USB-2-Serial converter in the standard USB port instead.  It might be cheaper/easier. Smiley

It isn't easier or cheaper than using what's already there, and doesn't take one of the two available USB ports.  Interfacing with USB would require additional parts, when interfacing with the 3.3v async lines wouldn't if what I'm attaching already uses 3.3v signaling.
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caseih
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« Reply #8 on: May 03, 2010, 08:54:38 AM »

If you are adding the JTag device to allow an application to use the RS232 port (not for debugging purposes), you could use a USB-2-Serial converter in the standard USB port instead.  It might be cheaper/easier. Smiley
For me I need the serial port for the serial console so I can tftp boot and things so I can write a new distro to the flash.  The JTAG device is simplest for now.  I bet, however, that for a few dollars I could rig up a board to convert the serial lines on the guruplug to a regular (albeit 4-conductor) serial port.
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daemondust
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« Reply #9 on: May 03, 2010, 08:58:28 AM »

There are lots of options for a USB to 3.3v Async serial.  http://www.sparkfun.com/commerce/product_info.php?products_id=718 for one, though there are MANY others.
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