The ZX Spectrum is back! Rejoice!

By Gareth Halfacree. Posted over 6 years ago.

Sinclair’s original ZX Spectrum, launched in 16kB and 48kB flavours in 1982, was the great success story of the British computing industry. Selling five million units over its lifespan, the low-cost colour microcomputer is credited with launching the careers of some of the biggest names in gaming.

The ZX Spectrum Next, by contrast, is a device unlikely to sell five million units. The brainchild of Henrique Olifiers, its production funded by a barnstorming Kickstarter campaign last year, the ZX Spectrum Next is, at its heart, a clone of the ZX Spectrum – one officially licensed by Sky In-Home Services, the current holder of the Spectrum and Sinclair Computers intellectual property – with some serious upgrades.

Where the original ZX Spectrum was based on a Zilog Z80-compatible 8-bit processor, the Next uses a modern field-programmable gate array (FPGA), a chip that can be programmed to replace almost any other chip. Using files known as ‘gateware,’ this FPGA acts as the Z80 along with the other components that made up the original Spectrum and, with the press of a key, any of its various successor devices.
With plenty of room to spare – the Z80 being a relatively simple device by modern standards – the FPGA is also used to power some of the Next’s additional features, which range from an SD Card slot from which programs can be saved and loaded, to a trio of FM sound synthesis chips, which upgrade the original Spectrum’s beeps and boops to multi-channel audio.

The Next isn’t an emulator, though. Each of these FPGA ‘cores’ is a functional recreation of the original chip, running exactly like real hardware. The result is a device which is, with very few exceptions, completely compatible with both software and hardware made for the original Spectrum – including plug-in cartridges and, with time taken to cut holes for the additional ports present on the Next, the original ZX Spectrum 16/48kB casing and keyboard.

zxspectrumnext-accelerator

The Next’s upgrades don’t end with the FPGA, though. Where the original Spectrum had low-quality RF-modulated video output which could, with a small modification, be converted to slightly improved composite video, the Next includes crystal-clear digital HDMI and analogue VGA outputs. There are two joystick ports as standard, with room for another two, and connectors for the original ‘dead flesh’ Spectrum keyboard or a more modern external PS/2 keyboard. There’s even 1MB of RAM, upgradable to 2MB, which sounds limited by modern standards, but is a vast improvement on the 128kB maximum available on a stock Spectrum.

Expanding horizons

If that list weren’t enough, hardware designer Victor Trucco decided to keep on adding more: a header on the board makes room for a low-cost ESP8266 WiFi module for network connectivity, while there’s space for a real-time clock module to be soldered in place. An ‘accelerator’ header even allows a Raspberry Pi Zero to be connected to the Next for use as a co-processor board – albeit one which dwarfs the system’s primary hardware in speed and memory capacity.

Using the Next is by and large a pleasure. FPGA cores and the custom-written NextOS operating system are loaded onto a full-size SD card and inserted into the Next, which is then connected to a 9 V power supply – not, sadly, included in the bundle, and woe betide anyone trying to use an original Sinclair power pack, as a switch in polarity means you’ll be left with a dead Next.

With power, display, and a keyboard connected, the Next boots into its operating system and displays a friendly menu through which the BASIC programming language, CP/M operating system, or image files from tapes or disks can be loaded. As a fully-compatible Spectrum clone, there’s also an option to load original media: the 3.5 mm audio jacks are present and correct, allowing for easy connection to a tape deck.

Original Spectrum software runs perfectly on the Next, and two accelerated modes – which switch the Z80 core from its stock 3.5 MHz to 7 MHz or 14 MHz, with a planned 28 MHz mode temporarily removed for stability reasons – make games that would have struggled originally, such as those based on the Freescape 3D engine, tick along impressively quickly.

zxspectrumnext-bitmapdisplay

Looking ahead

Some of the Next’s promised features, though, are not yet available. Software to make use of the optional Raspberry Pi Zero accelerator board or ESP8266 network module has yet to be written, and while the Next has the ability to display 256 colours at once and control hardware sprites, these features are limited to simple demos.

A bigger issue than unfinished software is a hardware flaw in the board revision – 2A – sent to crowdfunding backers, whereby a lack of smoothing capacitor on the 9 V regulator causes noise on the power lines bad enough, in some cases, to cause instability. Thankfully, that’s a relatively simple fix and one which is fully resolved in the 2B variant, which will be shipped to new customers and to those picking up the cased version of the Next, housed in a keyboard chassis custom-designed by Sinclair’s own industrial designer Rick Dickinson.

At £142.80 uncased, and £252 cased (both inc. VAT), the Next is an expensive trip down memory lane – but one which ticks an awful lot of boxes and, with a little work on the software front, could bring joy to hackers of a certain vintage for many years to come.