arleybls/zx-sizif-xxs

Smallest ZX Spectrum clone with real Z80 and FPGA

Sizif-XXS

Smallest FPGA-based ZX Spectrum clone with real Z80.

Tech specs

• Two PCB varians: 100x24.5mm (main version) and 65x30mm (Zero version) - both are functionally identical, differs only in size
• PS/2 keyboard
• Pentagon, Spectrum 128, Spectrum 48 and Spectrum +3e modes
• Altera EP1C3T100 FPGA
• Real Z80 with 3.5MHz, 4.4MHz, 5.2MHz, 7MHz (no-wait turbo) and 14MHz (turbo with wait-states) modes
• 512K RAM
• TurboSound with switchable stereo ABC/ACB/mono output
• Integrated DivMMC and Z-Controller, 1x microSD socket
• PAL video output (AV cable like in Raspberry Pi)
• ULAplus
• SpecDrum
• Covox (Pentagon standard - port #FD)
• SounDrive (4-channel stereo covox - ports #0F, #1F, #4F, #5F)
• Tape input via 3.5" jack
• USB 5V power supply

Magic button

Sizif has a number of configurable parameters that you can change on the fly. To do this just hold Magic button for a second.

To navigate menu you can use up-down keys, to change value use enter or left-right keys. Kempston, Sinclair, Cursor and QAOP supported.

If you press Magic button for a short time, the standard NMI handler 'll be called.

PS/2 keyboard buttons

Button	Function
F1	Pause
F5	Magic button
F10	Reboot
F12	Reboot
Ctrl+Alt+Del	Reboot
Ctrl+Alt+Backspace	Reboot
Numpad 8, 2/5, 4, 6	Joystick's up-down-left-right
Numpad 0/Enter	Joystick's fire
Alt	Joystick's fire

RAM

Sizif contains 512K RAM. 128K available via 7FFDh port, 128K via DFFDh (Profi standart, most compatible with old 128K software) and 128K used for DivMMC. Remaining space used to store ROM. Note that DFFDh port available only in Pentagon mode.

SD card

Sizif have preinstalled esxDOS firmware, which provides ability to load TAP, TRD, SCL, Z80 files and save snapshots. To use this you should format SD cart to FAT32 or FAT16 and unpack latest esxDOS release (link) to card. Also it's recommended to install Long Filename Browser (link) to card.

How to program

There is two options:

1. Program via JTAG connector using USB blaster and Quartus Programmer - use jic file from out folder.
2. Program flash chip directly using TL866 or similar device - use bin file.

Changelog & current status

• Rev.A - first release. Please note the errata.
• Rev.B:
  • fixed all rev.A issues
  • fixed "jailbars" on video output
  • 0805 footprints replaced with 0603
  • tape input moved slightly away to not to interfere with wide AV jack
  • 3.5 jacks replaced with THT variant for better reliability
  • changed ps/2 header orientation
• Zero Rev.A - first release of Zero version. Based on Rev.B of main pcb.