Add a Serial port to the PowerPC Linkstation

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Originally by frontalot and nix from linkstationwiki.org



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!

Most of this information courtesy of http://www.type-g.com, http://www.kurobox.com, http://www.tldp.org, http://www.larwe.com, and John Taylor.

Also look at: How to attach a serial port to the Kurbox/KuroboxHG


Contents

Prerequisites

  • (1)Electronic-grade soldering iron
  • (1) 0.015", 1 oz silver-bearing solder
  • (1) Desolder braid, solder sucker, or Servisol Soldamop
  • (1) 0.1” series PCB header plug, 4-way
  • (1) Serial converter (or build your own - see Stage 4)
  • (1) Tweezers
  • (1) Anti-static wrist strap

Stage 1 - 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:
The Circuit Board

Stage 2 - Attach Header to the Board

  • The console header needs to be attached to the J1 pad:
  • Remove the preexisting solder from J1:
  • Solder the PCB header to J1 so that the pinouts face towards the IDE header
Solder the PCB header to J1 so that the pinouts face towards the IDE header

J1 Pinout

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

Stage 3 - Enable Full Serial Tx/Rx

Method 1 (easier)

  • To enable write support across the serial port bridging r76 with a short piece of wire or just with some soldering
  • IN SHORT, ALL THAT IS NECESSARY TO GET 2 WAY SERIAL COMMUNICATION ON THE KURO HG, HD, AND PPC LINKSTATIONS IS TO BRIDGE THE CONTACTS FOR THE SERIES RESISTOR AT R76.

http://forum.buffalo.nas-central.org/viewtopic.php?f=42&t=9186

Method 2 (original)

To enable write support across the serial port, remove the 10K ohm pullup resistor from R75 and install it , or another 10K ohm pullup resistor, to R76. From http://www.larwe.com
  • To enable write support across the serial port, remove the 10K ohm pullup resistor from R75 and install it , or another 10K ohm pullup resistor, to R76.
HG hardware requires different procedure. Instead of adding 10K ohm, a short wire connecting two pads perpendicular to R69 worked for me (I replaced R69 with 10K ohms, you can keep the original part.)

Desoldering 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.

Stage 4 - The Serial Converter

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

Models other than KuroPro
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If you are attaching a serial header pin onto the main board, you may want to consider:

  • Using the header pin unit with a 90 degree bend, or you might not be able to close the case
  • Soldering it with the pins toward the interior, rather than toward the case. This allows easier access, since if the pins face the case side they would be very close to the metal side. This would make access is so tight that one might end up taking the board out to get plug fitted on the pins.


Build your own LVTTL/RS232 or LVTTL/USB interface

Buy your own TTL Level Shifter

Usage considerations for the TTL-232R-3V3

TTL-232R-3V3 USB to TTL Serial Converter Cable
A very similar TTL/USB converter cable that uses a chip by FTDI (the same chip is used in the SCON-KIT ) can be obtained, but the pinout at the connector end would need to be reassigned: Spec Sheet w/ pinout, wire colors & other info
MM232R.jpg Mouser Part # 895-TTL-232R-3V3 $20.00
4pinheader.gif Mouser Part # 517-929400-01-04 $0.32

A working/tested pinout/wire-color scheme is:

Color Pin Number Signal
yellow 1 TXD
orange 2 RXD
unused 3 VCC
black 4 GND
  • Solder the 4-pin header to the board. Make sure you don't have shorts.
  • You will need to switch wires on the TTL-232R-3V3 cable. Use a sharp object to lift the plastic tabs and carefully pull the wires out. Rearrange them according to the table above (black, empty, orange, yellow, empty, empty) and slide those wires back in. Tape the other wires to make sure they don't short anything.
  • When plugging in the cable, make sure black aligns with GND, yellow with TXD, and orange with RXD.
  • Connect the USB cable to your computer, start a terminal program with the right settings.
  • Turn on the device, you should see output from the bootloader in couple seconds.

Stage 5 - 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