Hardware
BlueSCSI Hardware
This page exists to answer questions about what features exist in each version of BlueSCSI hardware, to call out hardware design decisions, and to provide some hardware tweaks which can resolve issues that may appear.
BlueSCSI Ultra
2025.10a
Features:
* DIP Switches for common configuration instead of using an INI file
* USB-C
* Switchable Termination (via DIP)
* Can back-feed the termination power rail
* Both Molex and Berg Floppy power connectors
* Integrated RP2350B chip
* Onboard buttons for both RP2350B flash (“BOOT”) and RP2350B reset (“RST”)
* GPIO Expansion Headers for WiFi, Front Panel Board, etc
* Built in header for I2S audio output board
* Drive activity LED header like BlueSCSI v2
* Now using more efficient buck regulators for both 3.3v (RP2350B power) and SCSI Termination (2.85v)
* Integrated polyfuses for over-current protection
* Input over-voltage protection (turns power off to the whole board)
* Ability to power the SD card off to reset communications
* New transceiver-based SD card communication system that can reach 83MHz in testing
* 4 layer PCB for better high speed signal integrity
Design Decisions:
* Talk to the SD card as fast as possible
* Revamp the power system and include more protection than ever before
* Expose every extra GPIO pin for additional use cases
* Maintain the PCB size and mounting bracket hole positions from BlueSCSI v2
* Power via Molex / Berg Floppy instead of termpower
BlueSCSI Ultra Wide
2025.10a
Features:
* 68 pin Wide SCSI
* DIP Switches for common configuration instead of using an INI file
* USB-C
* Switchable Termination (via DIP)
* Can back-feed the termination power rail
* Both Molex and Berg Floppy power connectors
* Integrated RP2350B chip
* Onboard buttons for both RP2350B flash (“BOOT”) and RP2350B reset (“RST”)
* GPIO Expansion via flex cable for Front Panel and other uses
* Built in header for I2S audio output board
* Drive activity LED header like BlueSCSI v2
* Now using more efficient buck regulators for both 3.3v (RP2350B power) and SCSI Termination (2.85v)
* Integrated polyfuses for over-current protection
* Input over-voltage protection (turns power off to the whole board)
* Ability to power the SD card off to reset communications
* New transceiver-based SD card communication system that can reach 83MHz in testing
* 4 layer PCB for better high speed signal integrity
Design Decisions:
* Talk to the SD card as fast as possible
* Revamp the power system and include more protection than ever before
* Expose every extra GPIO pin for additional use cases
* Maintain the PCB size and mounting bracket hole positions from BlueSCSI v2
* Wide SCSI
* Power via Molex / Berg Floppy instead of termpower
Desktop 50 Pin
2023.10a
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
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
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
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:
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:
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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