The ‘Interface 1bis’ is the only ZX Spectrum (48,128,+2,+3) expansion device that features the combined functionality of
- Remote storage, of unlimited size, with long filename support, on a server machine, connected via a full-speed USB port.
- Non-volatile 128 KB RAM drive, for application that need to store data frequently and fast.
- Kempston joystick port.
Following devices are also supported by the operating system and are automatically identified, when attached to the mouse connector:
Asynchronous serial communication cable, with or without a RS232 trans-receiver
Serial printer, through a RS232 trans-receiver
Parallel printer, through a serial to parallel adaptor
'EAR' cable for rendering tape files as audio signal
- Ethernet connectivity, by means of an optional, third party, add-on module.
- Enhanced 'Extended BASIC' with comprehensive random-access file handling capabilities and full emulator (.SCR, .TAP and .Z80) files support. Files in .TZX format can be loaded either directly, if they contain only standard speed blocks, or otherwise, using the built-in 'tape player' and the 'EAR' cable.
- Integrated Game Browser and File Manager, with mouse and joystick control, being able to access besides the on-board SD card and a server PC, connected to the USB port, up to seven networked 'stations', which can be PCs or 'Interface 1bis' units, over the Internet, as well as the games und utilities archive of the 'Word of Spectrum' site.
The navigation functions include jumping to a given display page as well as advanced search facilities.
When a game is downloaded from the 'Word of Spectrum' archive, the associated screenshot, info and POKE files are also retrieved and transparently linked to the relevant game. The POKEs management functions allow the selective enabling of 'trainers', that are automatically applied when the corresponding game is launched.
Both 48k and 128k snapshots can be created without interrupting the game, just by pushing the interface's button. The application manages snapshots transparently to the user, maintaining always two different copies in order to allow both restarting the game from the last 'good' situation, in case of unsatisfactory progress, or securing the attained progress.
The application can perform the full range of file management functions, including complex ones, like moving entire directory trees, between any 'locations', be they 'Interface 1bis' units or PC servers, around the world.
The key to its versatility is the distinctive architecture of the IF1bis, which offloads all peripheral I/O operations onto a microcontroller, connected directly to the system’s data bus. This simplifies the design to a great extent and in conjunction with a rationalized memory configuration, requiring just one 32KB non-volatile SRAM chip, adds considerable benefits like:
- Small PCB size, of under 0.5dm2, allowing a
- Zero desk foot-print, due to vertical mounting.
- Simple, two-layer, PCB layout with very short tracks, for reduced noise.
- Low power consumption: at under 75mA, the lowest among comparable devices
- Low bus load: unequalled at only 0.7µA data bus leakage and only 0.5µA plus 1 (one) standard CMOS load on the other lines.
- Improved peripheral device handling, as the microcontroller, with its multiple hardware timers and complex interrupt logic, is specialized and better equipped for this task than the ZX Spectrum’s CPU.
- Simplified operating system, needing only one device driver: for the ‘Parallel Slave Port’ of the microcontroller, which in turn handles all low level peripheral control operations.
The IF1bis has certain special features, not encountered on comparable devices, as no compromise on robustness was made in the process of optimizing the performance / cost ratio:
- The control push-button is de-bounced and multiplexed using a dedicated microcontroller, which generates clean, digitally timed, RESET and NMI signals.
- The /ROMCS line is driven not through transistors, but a Low-Voltage CMOS buffer, to ensure fail-safe memory paging.
And last, but not least:
- The IF1bis does not rely upon the host machine's CLK line, which on some ZX Spectrum models is unusable.
The ‘Interface 1bis’, as the name intends to suggest, is 100% software (backward-) compatible to the ‘ZX Interface 1’ of Sinclair Research, in respect of ‘Microdrive’ storage operations, as well as RS232 and ZX Network communication, both at BASIC command and ‘hook code’ level, yet not in 128k BASIC mode.
All file handling operations can equally be performed on any of the two implemented file systems:
- file device, for a PC server (device "V"),
either local or remote, over an IP network.
The main enhancements to the ‘extended BASIC’ of the original ‘ZX Interface 1’ are:
- The file size limit is 16 MB.
- Sequential access is not restricted to ‘PRINT’ files.
- Data in memory can be read, written or verified, through direct random access, to (or from) a specified position in a file, of any type, without the need to OPEN it.
- Abbreviated syntax, allowing the omission of the ‘device type’ and ‘drive number’ fields in a statement, if they are the same as in the previous one.
The operating system of the ‘Interface 1bis’ has a very long development history, being written in 1994 and since then constantly improved and adapted to new hardware configurations. It is a mature, stable product, tailored to practical needs and offering arguably unrivalled functionality, speed and ease of use.