Add Serial Port

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Revision as of 06:24, 8 July 2006 by Jkk (Talk)

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WARNING!

There is a possibility that you could brick your NAS with these instructions. Please make sure that you read the entire page carefully. Adding a serial port requires soldering onto the Kurobox main board and can cause catastrophic failure to the hardware.


Contents

Getting Started

Locate J1 on the Mainboard

Locate J1 on the Mainboard after removing it from the case. This should be a 4 pin unpopulated header. The easiest way to find this is to first find the CPU first, and then look near the corners for J1.

Attach the serial port

J1 Pinout
Pin Signal
1 Transmit (TX)
2 Receive (RX)
3 Power (3.3V)*
4 Ground (GND)

The manufacturer of the Kuro filled the jumper holes for the Serial port with solder. Removing the solder from the jumper holes on the Kuro board is simple.

  • Press the tip of a 15 watt soldering iron with a good sharp tip (if the tip isn’t sharp use a file to sharpen it and tin the tip) into the hole from the back of the circuit board.
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WARNING!

THIS IS VERY IMPORTANT. IN THE NEXT STEP THE BOARD SHOULD BE BETWEEN THE SOLDERING IRON AND YOUR MOUTH. FAILURE TO PLACE THESE THREE OBJECTS IN THE CORRECT ORDER WILL RESULT IN EXCESSIVE PAIN.


  • When the solder is flowing nicely, get your mouth about 1" from the front of the board and blow hard into the wet solder while at the same time removing the solder iron. You will blow the solder out of the hole leaving a hole that you can easily put a wire through.

Single or Bi-directional Traffic?

To allow one-way serial port traffic (read only) you can just add the 4 pin header and be done. To enable bi-directional serial port activity, you must also add a 10K resistor as described below.

Enable Write Mode (optional)

This step is optional, but you might find that the serial port is more useful with bi-directional traffic. To enable write support across the serial port, remove the 10K ohm pullup resistor from R75 and solder this, or another 10K ohm pullup resistor, to R76.

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TIP

To desolder an SMD resistor you can apply the following trick:

  • Take a short piece of blank wire and bend one end into a small U-shape using some small pliers. The U-shape should be as such that you can touch the sides of both ends of the resistor at the same time. The width of the U should basically be the length of the resistor.
  • Wrap the other end of the wire around the tip of your soldering iron - while it is still cold. You now have a small U-shaped tool to remove the resistor.
  • Heat up the iron. When the wire is hot enough, heat up the solder at both ends of the resistor and gently pull the resistor away from the pads with the U-shaped tip. Be careful, the resistor likes to end up on the floor.

Level shifter

The serial port signals from the processor are only 3.3V. For proper RS-232 5V signaling, an RS-232 level shifter needs to be added. These are very common in PDA serial cables also, but can be purchased from Compsys Bench

Item Name: A232DBH3v Max232 3.3v ver. adapter assembled w/hood kit 
Item Number: A232DBH3v 

As an alternative you can make the level shifter cable yourself: Circuit Console Cable.pdf (courtesy Type-G). Components can be found at e.g. Digikey

You can also etch a circuit board which makes building the interface and installing the interface really easy. Instructions are Here.

The Interface should be attached as close as possible to the board. The signals are very weak and wires as short as 2" (5 cm) have been reported to cause data loss across the serial port.

If you use the Compsys level shifter you should remove the 9 pin D connector from the shifter and solder the transmit and receive pins directly to the new header. This makes the shifter sit directly above the circuit board and makes the wires as short as possible. You will need to use 2 short (about 3/4", 2 cm) pieces of wire to connect the power and ground connections on the level shifter to the header. Next you should connect 6" (15 cm) pieces of wire to the transmit, receive and ground connections on the RS-232 side of the level shifter and route them to the 9 pin D connector which can be mounted on the rear of the Kurobox. Here's a photo of the level shifter and a photo of the connector on the back of the Kuro.

Note that the Compsys level shifter is designed to be used on a client device as opposed to a host device. As such it has the wrong gender 9 pin D connector. it also has the transmit and receive pins switched on the serial connector. This may not be an issue depending on what you plan to do with the serial port. If you plan to connect it to your computer for monitoring the console messages, you can just use a straight through cable. It will become an issue when you start connecting periferals to it as the connector will not mate with your periferals. You have two options in this case. the first is to buy a null modem connector to sit between the Kurobox and your periferals. The second option is to replace the connector with the correct connector and switch the wires on pins 2 and 3.

Once you have the level shifter installed you should be able to see console messages via the serial port.

Serial Port Settings

Data Settings 
Baudrate  57600
Data bits  8
Stop bits  1
Parity  None
Flow Control  None

External Links