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blue-gs/POWERING_BLUE-GS.md

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Powering BlueGS

There are 4 ways to power your BlueGS board, listed here from "most easy" to "least easy".

Termination Power from SCSI card

If your SCSI card provides Termination Power, then you only have to BlueGS to your SCSI card using the included flat 26-pin cable or DB-25-M connector. No additional steps are required, and BlueGS should turn on the moment that the computer is powered up.

Termination Power from another SCSI device

If your SCSI card does not provide Termination Power, then you can provide the necessary power through another SCSI device connected to the DB-25 connector.

Most external SCSI devices will provide the necessary Termination Power. To power BlueGS this way:

  • Connect the new SCSI device to the DB-25 connector
  • On BlueGS, switch "Termination" to "off"
  • Ensure that the new SCSI device is terminated, either via a switch (if it has one, such as on the IOmega Zip Drive) or an external terminator that connects to one of the SCSI ports of the device.

This external device must be powered-on before the IIgs turns on.

+5V from inside the computer

You can power BlueGS via the "Aux 5V Power In" connector, using a 5V source in your computer. This can be from the Game IO port, a card slot, or a tap from the power supply rail.

If you power BlueGS using this connector, it will also send termination power to any other devices on the SCSI bus that may need it -- such as another BlueSCSI device!

Older versions of BlueGS could be powered by the 12V fan connector in the IIgs, but that has been removed in 1.4 and higher.

USB port on Blue Pill board

You can power BlueGS using the USB connector on the Blue Pill module as long as you are not also using SCSI Termination Power or 5V aux power.

Why can't I use USB while BlueGS is powered from SCSI or Aux?

There is a design flaw on the Blue Pill board where power sent to the +5V pin of the board can then be sent back through the USB connector. This "backflow" can potentially cause damage to whatever is providing USB power and so it strongly recommended that you do not use USB to power BlueGS while connected to SCSI Termination Power or aux power.

If there is no termination power on your bus and BlueGS is not using the aux power connector, then there is no danger of "backflow" and USB power can be used.

What is Termination Power?

Very briefly, "Termination Power" is electrical current that is used to power devices called "Terminators". A "Terminator" is a device connected to the end of a "bus" (the cable/wire) to show where the end is.

If you think of the SCSI bus as a water pipe and each drive on the bus as a water tap connected to the pipe, then a Terminator is the cap at the end of the pipe.

What SCSI cards do/don't provide Termination Power?

While many SCSI cards do not provide termination power, there are some that can be modified to that they will.

Cards that DO provide Termination Power

  • GGLabs A2SCSI
  • RAMFast SCSI - controlled by JP1 or DIP #1, see manual for details

Cards that DON'T provide Termination Power

  • Apple Rev B SCSI
    • Can be modified to provide termination power
  • Apple Rev C SCSI
    • Can be modified to provide termination power
  • Apple High-Speed SCSI ("Sandwich II")
    • Can be modified to provide termination power

Unknown cards

  • AMR SCSI
  • CMS SCSI II
  • Cirtech SCSI/InSyder
  • GSE-Reactive SCSI Card
  • SVA Hard Disk Adapter

How can I tell if my SCSI card is providing Termination Power?

If your card is not in one of the lists above, then the easiest way is to connect BlueGS and see if it turns on when the the computer is powered on.

If you have a multi-meter, you can check the voltage on pin 25 of the DB-25 connector. If termination power is provided, this pin should read between 4.5 and 5 volts.