Xberry Pi

The Xberry Pi (XBP) is a ZX Spectrum Next clone using a PCB that has approximately the same dimensions as a Raspberry Pi 3.

This page documents key info specific to the Xberry Pi that is not covered by the documents in its github repository. The schematics for the XBP are available in its github repository but its gerber and PCB CAD files are not currently publicly available.

Ports and headers for Xberry Pi model 4G

Note that some of the ports and headers have different names on older revisions.

• BT1 - RTC battery clip location, not attached in above picture.
• J1 - Micro USB power input.
• J2 - HDMI digital AV output.
• J3 - PS/2 keyboard/mouse input.
• J4 - 3.5 mm headphone output.
• J5 - Sega Mega Drive / Genesis compatible joystick port.
• J6 - Raspberry Pi Zero accelerator header.
• J7 - Matrix keyboard headers plus reset, NMI and divMMC NMI button headers.
• J8 - WiFi adapter header.
• J9 - JTAG debugging header.
• J11 - Joystick select header.
• J12 - VGA video output header.
• J15 - 3.5 mm microphone input for a cassette tape player.

Differences between the XBP and the ZX Spectrum Next KS1

The XBP is mostly identical to the ZX Spectrum Next KS1 but with the following differences:

• The XBP uses the much smaller Raspberry Pi 3 SBC form factor.
• No expansion slot.
• No integrated keyboard. A header is provided for connecting a Matrix keyboard.
• No second joystick port. A joystick splitter is available for a second joystick port.
• No footprint for adding a second SD card.
• No reset or NMI (Non Maskable Interrupt) buttons are on the XBP PCB. Footprints are provided for you to add these buttons if desired but these functions can be accessed via function keys.

Differences between the XBerry Pi 5D and earlier versions

Version 5D of the XBP introduced some notable changes:

• The XBP 5D uses micro HDMI instead of HDMI like on previous versions.
• USB-C power connector instead of Micro USB.
• Support for a second joystick port on a daughter board.

PS/2 input configuration

A PS/2 splitter cable can be used to attach a PS/2 keyboard and mouse to the XBP simultaneously.

You cannot use your PS/2 keyboard after booting a new installation of NextZXOS on a XBP. This is because NextZXOS is designed for use on official Next computers and NextZXOS defaults to using the integrated keyboard. To fix this you have to edit MACHINES/NEXT/CONFIG.INI on your NextZXOS microSD card and change the ps2 option from 1 to 0:

ps2=0

To enable PS/2 mouse input, you must enter the Next boot configuration menu by pushing the SPACE bar during boot and check the PS2 option is set to Mouse.

Joystick port splitter

XBP revision 5D supports a second joystick port on a daughter board. Previous revisions require the use of a joystick port splitter to connect a second joystick or joypad.

You can download the PCB gerber files and the BOM for building a joystick splitter yourself from the XBP github repository. You can also buy a splitter pre-assembled from PCBWay. stl files for printing a splitter case can be downloaded from Thingiverse.

The splitter needs two jumper wires (DuPont cables) to be run from either J11 or J13, depending on your XBP version, to header J4 on the splitter. It is the 2 pin header that is nearest to the joystick port, you may have to solder a jumper header if you want to use a joystick splitter. These wires carry the 3.3V power and the JoySelect signal. Without connecting these wires, only the first joystick port will work.

Modifying Raspberry Pi cases

You should be able to fit the Xberry Pi versions pre 5D into most cases designed for the RPi 3. Version 5D should fit into RPi 4 cases after removing the daughter board but a few small adjustments are often required before the PCB will fit into most Rpi cases. There is insufficient space to install the Pi Zero add-on board within most RPi cases.

You will need to use a grinder or a similar tool to create a new hole for the XBP's mic input jack. For the 5D and Rpi 4 cases you may need to enlarge the second micro HDMI hole a bit so that the EAR/MIC connector can be properly accessed., if you want to load programs from tape. In some cases you may also need to remove a bit of plastic that separates the network socket from the USB ports, if there is one present on your case to make room for the joystick port and you may need to remove another separator tab if running a joystick splitter cable into the case.

Recommended power supplies

Power supplies known to work with the RPi 3 such as the official RPi 3 USB power supply should be good enough to power pre 5D XBP models. Your PSU must use a Micro USB connector or USB-C for version 5D and provide at least 5V 2A for reliable operation.

The XBP doesn’t have a power negotiation circuit so you should use a PSU of the correct rating to avoid causing damage.

Known hardware issues and fixes

The XBP suffers the same HDMI backpower issue as the Spectrum Next KS1. This issue causes the XBP to fail to power cycle correctly when using HDMI. The workaround is to buy an inexpensive HDMI splitter which allows you to disconnect your XBP from your HDMI display at the push of a button without having to remove and re-insert your HDMI cable every time you want to power cycle the machine such as when you want to enter the boot configuration menu, update your firmware or boot a different core.