The tranZPUter^FusionX is a spinoff concept from the tranZPUter series. It shares the same purpose, to replace the physical Z80 in a Sharp or similar system and provide it with features such as faster CPU, more memory, virtual devices, rapid application loading from SD card and by using a daughter board, better graphics and sound. The FusionX board can also be used to power alternative CPU's on the host for testing, development and to provide a completely different software platform and applications. It can use the underlying hosts keyboard, monitor, I/O and additionally better graphics and sound provided by the FusionX. It shares similarities with the tranZPUter^Fusion but instead of realising it in hardware via an FPGA it realises it in software as an application. This is made possible by a SOM (System On a Module), not much bigger than an FPGA device yet provides an abundance of features, ie. dual-core 1.2GHz Cortex-A7 ARM CPU, 128MB RAM, 256MB FlashRAM, Wifi, HD Video, SD Card, USB port and runs the Linux operating system. Using the same base design as the tranZPUter^Fusion it incorporates a CPLD to interface the Z80 host to the SOM and provide cycle accurate Z80 timing. The SOM interfaces to the CPLD via a 72MHz SPI channel and an 8bit bus to query signal status and initiate Z80 transactions. In Z80 configuration, a Linux Kernel driver instantiates a Z80 emulation which realises a Z80 CPU in software which in turn can command and control the host system. The kernel driver along with a controlling application can provide a wealth of features to the host through this mechanism. The SOM is also connected to an SD Drive and USB 2.0 port so there is no limit to features which can be proivded. Like the tranZPUter^Fusion, the tranZPUter^FusionX can provide enhanced video and sound to the host. The SOM incorporates dual DAC audio and a 2D GPU with configurable resolutions switched onto the hosts video and audio outputs under software control. The FusionX board is ideal for any developer wanting to physically program and interact with retro hardware using a Linux platform with Wifi and USB/Serial port connectivity. To most retro users, in the early stages of FusionX development, the board wont have much use. As the project matures, a board can be obtained and installed into the Z80 socket of their Sharp or simlar Z80 based system (providing there is sufficient room to accommodate this board) and utilise the upgraded featues, such as:

• Original host specifications
  - the machine behaves just as though it had a physical Z80 within. There might be slight differences in the Z80 functionality as it is implemented in software but the Z80 hardware timing is accurate.
• Accelerator
  - the Z80 can run at much higher speeds due to the abundance of memory and 1.2GHz dual-core processor, which would typically see performance upto that of a 500MHz Z80.
• Emulation
  - emulation of all the Sharp MZ series machines, experiencing it through the host system keyboard, monitor and I/O.
• Graphics
  - all original Sharp MZ graphics modes, regardless of host, including additional resolutions upto HD are available through GPU configuration and these can be selected and programmed on the host in languages such as Basic.
• Sound
  - the host will have access to the stereo DAC converters, which can playback 48KHz CD quality sound or emulate the SN76489 or basic bit/timer sound of the Sharp series. Sound recording is also possible via the Mic input.
• Processors
  - there are many software CPU implementations which can be ported to run on this platform, for example the ARM platform CPU emulations of the BBC PiCoPro can readily be ported. This in turn allows the potential for other machines, using the SOM advanced graphics and sound as necessary, allow emulations of machines such as the BBC to run on this Sharp host.
• Linux
  - using the host keyboard, speaker, monitor etc, a full blooded version of Linux, including Wifi, can be utilised at the host console.

Version 1.0 is the first official release of the tranZPUter^FusionX design. The FusionX board builds on a tried and tested Z80 host interface using the Altera 7000A MAX CPLD device. The CPLD not only interfaces the 5V Z80 host signals to the 3.3V signals on more recent devices, it also embeds the logic to perform accurate Z80 timing using a 50MHz clock to sample the Z80 host clock and activate signals according to the published Z80 state diagrams. In addition the FusionX includes a SigmaStar System-On-a-Module, this is a small 29mmx29mm stamp device which incorporates a dual-core Cortex-A7 CPU, 128MByte DRAM, 256MBytes FlashNAND and a Wifi transceiver. The SigmaStar SOM is capable of outputting 2D Graphics in an RGB 888 format with selectable resolution upto HD format. It is also capable of stereo audio DAC output at 48KHz. Click to view the full SigmaStar product brief. Using the experience gathered on the tranZPUter SW-700, a 30bit Video DAC is chosen to render the SigmaStar SOM video rather than a 2R-R ladder and additionally an 8bit DAC is included for rendering monochrome monitor contrast levels to cater for colour shading on monochrome CRT monitors as found in the MZ-80A/MZ-2000. The hardware design centers on a main circuit board which holds all the primary circuitry and a number of daughter boards, each daughter board dedicated to one host (ie. MZ-700, MZ-80A, MZ-2000). The daughter board intercepts the host video/audio subsystem and supports switching of the host video/audio and the mainboard video/audio to the monitor/speaker of the host. The mainboard can be used without daughter boards, the latter are only used when the SOM Video/Audio is required. This section outlines the mainboard schematics and circuit board design of the tranZPUter^FusionX.

The schematic interfaces the Z80 to the CPLD. The CPLD is 5V tolerant and operates internally at 3.3V. The outputs are selected as Low Voltage TTL meaning a '1' is represented by 3.3V as opposed to 5V in the host system. The specifications of 5V TTL see the switching threshold at approx 2.4V, thus the CPLD is able to drive 5V circuitry and with sufficient drive current, 25mA per pin. The CPLD internal state machines are clocked by an external 50MHz oscillator, this allows for adequate sampling and state change for a typical 1MHz - 6MHz Z80 host.

The SOM is rich in peripherals and this circuit interfaces some of them for use in the FusionX, these include:

• Stereo Audio Microphone input
  - a digital microphone input is also available but the pins are used in the CPLD interface.
• Stereo Audio DAC output
  - dual digital to analogue converters for sound output which can be clocked at 48KHz.
• WiFi Antenna
  - a SSW101B 20/40MHz IEEE 802.11 b/g/n/e/l/n/w WiFi transceiver operating in the 2.4GHz band with a 500M range. The SOM also includes a 100MHz ETH PHY but this is not used in this design as hard wired ethernet is not practical for a board which is sited inside a retro machine.
• USB Serial
  - when running Linux, the console is presented on a UART serial device. This serial device is converted into USB for ease of use to view and connect with the Linux console.
• USB
  - a Linux connected USB port allowing for device expansion, such as additional storage, mice etc.
• Fast UART
  - high speed full duplex with hardware handshake UART.
• UART
  - standard 2 pin UART operating upto 500KHz.
• SD Card
  - the SOM has inbuilt FlashNAND so can accomodate a simple Linux filesystem, addition of an SD card allows for greater storage of Host applications and Linux utilities. An SD card also makes for ease of upgrades as the SOM will auto upgrade when a suitably prepared SD card is present on boot.

The SOM outputs TTL RGB with 8bits per colour. This is interfaced to a 30bit VideoDAC with the lowest 2 bits, per colour, controlled by the CPLD. In addition, in order to drive the internal monochrome monitors of the Sharp MZ-80A/MZ-80B/MZ-2000 an 8bit VideoDAC is added which outputs a video signal in the range 4V-5V using a 332 RGB colour input, the colour input being the MSB of the SOM 888 TTL output. I term this the Contrast DAC, as it is sending the video signal with colour information as a voltage controlled contrast signal which presents itself on the monitor as differing contrast levels, thus simulating colour as grey levels. In order to get true black, the CPLD creates a blanking signal, MONO.BLANK, which is paired with a MUX 0V clamp on the daughter board which drives the monochrome monitor, this sees the RGB332 as 0V when 00000000 is present, then varying between 4.01V-5V when non-zero.

The power supply, for the SOM and CPLD, converts the 5V present on the Z80 socket into 3.3V using a high efficiency buck converter. This is necessary to minimise heat and provide maximum current to the SOM/CPLD. Additionally, a software controlled USB power switch is installed to enable (and reset if required) +5V power to the USB expansion port.

The final schematic is the interface between the SOM and the CPLD. Originally this was going to be a bi-directional 16bit bus with Read/Write and Strobe signals but after testing, the setup time for a 16bit signal with tri-state switching was much slower than an SPI connection due to the GPIO register layout and operation within the SOM and the speed of the I/O operations within the SOM. The solution used is to have a bidirectional 72MHz SPI bus between the SOM and CPLD for transmitting Z80 transaction requests and an 8bit read only parallel bus for more rapid reading of Z80 Data and seperate Z80 state information.