Hardware

BlueSCSI V2 Hardware

This page exists to answer questions about what features exist in each version of BlueSCSI V2 hardware, to call out hardware design decisions, and to provide some hardware tweaks which can resolve issues that may appear.

Desktop 50 Pin

2023.10a

Interactive BOM

Features Removed:

  • USB-C power port
  • Micro SD slot

Design Decisions:

  • The 2023.09a board revision was deemed too expensive to move forward with as a long term solution, due to increased production cost, so a few things were removed and changed for affordability reasons
  • Moves Pico to the edge to use built-in micro USB port (Pi Foundation really needs to upgrade this to USB-C)

2023.09a

Features Added:

  • Initiator Mode
  • I2C connectivity
    • Note: By adding both Initiator and I2C to the Pico it introduced an edge case incompatibility with three known systems.
    • See: 2023.09a GPIO Constraints
  • Dual SD Slots, one Micro and one Full Size (Use only one at a time)
  • USB-C power port onboard

Features Removed:

  • Option Switch Jumpers (these have been basically unused)

Design Decisions:

  • The termination switch chip was discontinued, changed to using LVTH245 plus a discrete mosfet switch. LVTH handles 8 lines of termination and the mosfet handles the last one (SCSI uses two banks of 9 signals, and most chips these days only do 8 or 16 bits at a time).

2023.03a

Features Added:

  • Configurable external LED brightness

Design Decisions:

  • People were having issues making all LEDs work with the included LED output (too dim). This change makes LED brightness configurable.

2022.12a

Features:

  • External LED jumpers
  • Onboard power and activity LEDs
  • Option Switch Jumpers
  • Switchable Termination
  • Power Isolation Jumper (allows for USB power to the Pico without any draw from the host system)
  • Term Power Back-Feed
  • Single SD slot, Full Size
  • SCSI Bus Reset Button

Design Decisions:

  • Using Raspberry Pi Pico instead of embedding the RP2040

DB25

2024.01a

Interactive BOM

Features Added:

  • PCB is now only as wide as the DB25 connector

Features Removed:

  • S1 and S2 Option Switch Jumpers (these have been unused in the code)

Design Decisions:

  • Some Macs have their DB25 port too close to the Display output or other things
  • Make the whole thing narrower to try and stop collisions
  • Micro SD slot moved further into the PCB, less of the card sticks out now

2023.06a

Features Added:

  • About 30% shorter

Features Removed:

  • Switchable Termination (termination is now always on)
  • SCSI Bus Reset Button (using too much space)

Design Decisions:

  • Many people commented that the prior DB25 was too long. This version removes some features, but decreases the length substantially.

2022.11a

Features:

  • Switchable Termination
  • Option Switch Jumpers
  • Single Micro SD slot
  • SCSI Bus Reset Button

Design Decisions:

  • Kept switchable termination on this model to increase possible use cases
  • Using Raspberry Pi Pico instead of embedding the RP2040

PowerBook / 2.5 Inch SCSI

2023.10a

Interactive BOM

Features Added:

  • I2C connectivity

Features Removed:

  • Option Switch Jumpers (these have been basically unused)
  • SCSI Bus Reset Button (impossible to get to inside a PowerBook)

Design Decisions:

  • Updated to allow SMD-soldering the Pico directly onboard
  • Termination switch chip was discontinued, same design decision as Desktop in that regard

2022.11a

Features:

  • Onboard Power and Activity LEDs
  • Solder pads for external LED
  • Switchable Termination
  • Option Switch Jumpers
  • Single Micro SD slot
  • SCSI Bus Reset Button

Design Decisions:

  • Using Raspberry Pi Pico instead of embedding the RP2040

Centronics 50 Pin

2024.03a

Features Added:

  • Dual footprint design for SCSI termination voltage, accepts both static and adjustable voltage regulators
    • BOM is provided for both options in prod files
  • Termination Power Back-Feed from USB
    • Useful for certain interface adapters which require termpower to be fed by the hard drive

Features Removed:

  • Option Switch Jumpers (these have been unused in the code)
  • Switchable Termination (termination is now always on)
  • SCSI Bus Reset Button (using too much space)
  • Mounting screw location removed (using space, not very helpful)

Design Decisions:

  • Similar to DB25, the original C50 design was very long
  • Options were removed which were used uncommonly or not at all to enable the shorter design
  • Shorter by over 1cm

2023.03a

Interactive BOM

Features:

  • Onboard Power and Activity LEDs
  • Switchable Termination
  • Option Switch Jumpers
  • Single Micro SD slot
  • SCSI Bus Reset Button

Design Decisions:

  • Using Raspberry Pi Pico instead of embedding the RP2040

Using Raspberry Pi Pico instead of embedding the RP2040

We’ve chosen to use the Raspberry Pi Pico dev boards for BlueSCSI v2. This decision has allowed us to have even our first rev of the BlueSCSI v2 PCB work with a Pico 2 (RP2350) with Wi-Fi.

When BlueSCSI came out the Wi-Fi feature of the Pico was not available. We didn’t have to do any board redesign when the Pico-W came out.

Similarly when the Pico 2 and Pico 2-W were released we made some framework updates and were the first Pico2/RP2350 SCSI emulator.

The Pico boards provide a common platform and expanding features every few years, allowing users to get a “free” upgrade when new versions are released. Quality of Pico dev boards is great.

The Pi Foundation does not (currently) allow for us to directly purchase the RM2 Wi-Fi Module in a cost effective manor. Wi-Fi is a huge feature of BlueSCSI so we want to make sure all of or BlueSCSI boards have all of the features users expect.

There are challenges designing around this of course such as a more limited PIN count, but we’ve been able to work around this effectively, with one exception on three systems.

Hardware Tweaks / Fixes

Sleep Mode

It has been noted that older versions of BlueSCSI V2 Desktop and PowerBook have issues with waking from sleep mode on a variety of systems. This is caused by some “pull resistors” which were added to ensure a consistent initial signal state, but which apparently interfere with or confuse the system.

These issues were resolved in Desktop 50 Pin 2023.09a (and later), and PowerBook 2023.10a (and later). The solution was to “pull up” the oSEL and oBSY signals instead of pulling them down.

Important Note: These changes are intended make the older BlueSCSI versions wake from sleep without issues. But they have not explicitly been tested yet. They are based only on the schematic differences between older and newer BlueSCSI revisions.

Desktop 2023.03a and older:

  • Remove R23 (remove carefully to ensure traces are not damaged)
  • Add 4.7k ohm resistors from the indicated Pico pins as shown in the image below:
    D50_2022_12a_SleepRework

PowerBook 2022.11b:

  • Effectively identical to the above Desktop version
  • Remove R23 (remove carefully to ensure traces are not damaged)
  • Add 4.7k ohm resistors from the indicated Pico pins as shown in the image below:
    PB_2022_11b_SleepRework

2023.09a GPIO Constraints

When adding I2C and Initiator Mode - two features not seen together on other Pico based SCSI devices - due to GPIO pin constraints the SCSI signal pins have the behavior whereby asserting RST will also assert SEL. Testing on a wide range of systems was successful with this design and we moved forward with it.

This design decision will only cause compatibility issues in a very small number of systems. Known systems are: AS/400, CISC 9404-F10, and VaxStation 2000.

Work around

Use an earlier version than 2023.09a, any DB25, or PowerBook model. They do not have Initiator and I2C.

Modify your 2023.09a as described here https://github.com/BlueSCSI/BlueSCSI-v2/discussions/253

This constraint will be addressed in the next version of BlueSCSI.

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