Add a Serial port to the MIPS Linkstation

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Originally by frontalot and nix from linkstationwiki.org. Connection details for the LS2 by Kuroguy



The console is the text output device for system administration messages. These messages come from the kernel, from the init system and from the system logger. On modern small computers the console is usually the computer's attached monitor and keyboard. The LinkStation, however, doesn't have monitor output; instead, it uses a serial connection for console output. Not only does the serial console provide valuable debugging output, it also allows root access!


Contents

Prerequisites

  • (1)Electronic-grade soldering iron (think really small)
  • (1) 0.015", 1 oz solder
  • (1) 0.1” series PCB header plug, 4-pin
  • (1) Serial converter (or build your own - see step 4)


Access the Board

  • Disassemble the LinkStation.
  • Remove the main circuit board by removing the 4 mounting screws:
  • Place the circuit board on a static-free work area:


Attach Header to the Board

  • The console header needs to be attached to the J1 pad:
  • Remove the preexisting solder from J1:


J1 Pinout

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

Enable Full Serial Tx/Rx

To enable write support across the serial port, simply bridge R186.


The Serial Converter

Buy One

The serial port signals from the processor are only 3.3V. For proper RS-232 12V signaling, an RS-232 level shifter needs to be added. These are very common in PDA serial cables also, but can be purchased from SuperDroid Robots (#MCU-026-172) or CompSys (#A232DBH3v).

Build One

As an alternative you can make the level shifter cable yourself:

Shifter.jpg

Components can be found at e.g. Digikey
  • If you want to build your own serial converter, you will need the following parts:
  • (5) 0.1 uF tantalum capacitors
  • (1) MAX3232CPE IC (Maxim), 3V type, 16 pin DIL
  • (1) RS232 male socket
  • (1) Some perf board (about 1" x 1")
  • (1) Wire


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

This 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.



Enabling the Serial Console

As the LS2 only has a single serial port which is used by the AVR, it is necessary to enable the serial console. This is done by jumpering the pins of J2 and disabling the watchbog timer on startu (by pressing the red button and pwereing it up). It is easiest to install J2 on the back of the board as it will be accessible by removing the cover and not the board from the chassis. I used a red jumper so it can be easily located.


Using the Serial Console

  • You may access the serial console using Windows HyperTerminal (included with Windows) or TeraTerm Pro.

Serial Port Settings

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

External Links