SAM Coupé

The machine is based around a Z80B CPU clocked at 6 MHz and a 10,000-gate ASIC. The ASIC performs a similar role in the computer to the ULA in the ZX Spectrum. The Z80B CPU accesses selected parts of the large memory space in its 64 KB address space by slicing it into 16 KB banks and using I/O registers to select the memory pages mapped into each 16 KB bank.

The basic SAM Coupé model has 256 KiB of RAM, internally upgradable to 512 KiB via a connector on the main board accessible via a trapdoor underneath, and externally up to an additional 4 MiB, added in 1 MiB packs via the Euroconnector on the back of the system.

The computer has a direct connection for a cassette recorder for data storage but two 3.5 inch floppy disk drives can be installed within the case as well or externally using an interface.

The SAM Coupé was designed primarily for the UK market, and is designed around the PAL television standard, which refreshes at 50 frames per second. Unlike a standard PAL signal which is interleaved, the SAM is designed to emit two identically positioned fields at 50FPS, giving something closer to a 312P signal than the 625I broadcast television signals common in the UK at the time.

The display is surrounded by a large border area to provide a title-safe display zone for the CRT televisions of that era. The color of this region can be changed in software by using the BORDER port to select a color from the palette.

The SAM Coupé has four display modes:

• Mode 4 — 256×192, linear framebuffer, 4 bits per pixel (16 colours) = 24 KB
• Mode 3 — 512×192, linear framebuffer, 2 bits per pixel (4 colours) = 24 KB
• Mode 2 — 256×192, linear framebuffer, 1 bit per pixel with separate color attributes for each 8-wide block of pixels = 12 KB
• Mode 1 — 256×192, non-linear framebuffer, 1 bit per pixel with separate color attributes for each 8×8 block of pixels = 6.75 KB (arranged to match the display of the ZX Spectrum for backwards compatibility)

The 'attribute' modes borrow their design from the ZX Spectrum, where a bitmap is used to select between a paper and ink color from two groups of eight colors. The group to use is selected by a 'brightness' flag. The color block can also be set to 'flash' - that is, alternate between the two colors used for paper and ink.

All modes use palette-based Colour look-up tables, selecting from a palette of 128 colours. The palette values consist of 2 bits for each of the red, green and blue components as well as an extra bit which increases the intensity of all three components by a half-step (a 'brightness' bit).

The ASIC can be configured to generate interrupts when a line on the display is starting to be emitted, allowing video effects to be synchronised with specific display lines with little effort. By default, it will generate an interrupt for every frame. Typically this interrupt is used to double buffer the frame, read the keyboard/mouse state, and output music.

The interrupt state can also be polled directly from the ASIC's status register.

The Motorola MC1377P RGB to PAL/NTSC video encoder creates a composite video signal from the machine's RGB- and Sync-signals (output by the ASIC) for the RF modulator.

The non-standard SCART display connector includes both composite and RGB output, as well as signals to drive a 16-color TTL monitor.

Access to internal RAM was shared between the display and the CPU, with CPU accesses incurring a speed penalty (memory contention) as it was forced to waited for isochronous ASIC memory-accesses to complete. As a result, the SAM Coupé's CPU effectively ran only around 14% faster than the ZX Spectrum CPU, yet was required to do much more work in SAM's high-resolution modes to produce a similar movement on the display. A Mode 3 or Mode 4 screen uses four times as much RAM as a ZX Spectrum Mode 1 display, so four times the work had to be done in the same time when updating it.

A small compensation was the straightforward arrangement of colour pixels in this memory, instead of the ZX Spectrum's more limited display and attributes memory. Low-level graphics software operations could be much simpler than their Spectrum equivalents and therefore somewhat faster to execute.

The penalty of memory contention delay applied to all memory accesses to RAM, and not just to memory associated with the video circuitry (as in the case of the ZX Spectrum). Hardware sprites and scrolling would have greatly improved the performance of games, unfortunately there was insufficient wafer space on the VLSI ASIC to include such circuitry.

While the main 256×192 area of the screen was being drawn, the processor could only access memory in 1 out of every 8 t-states. During the border area this was 1 out of every 4 t-states, which had no effect on the many instructions whose timings were a multiple of 4. In modes 3 and 4 the display could be disabled completely, eliminating these memory contention delays for a full 6 MHz running speed. Code running in ROM or external RAM was unaffected by contention, though any RAM accesses they performed to shared internal RAM would still be affected.

Six channels of 8-octave stereo sound are provided by a Philips SAA1099 sound generator chip.

This sound chip can also produce two 4-bit sampled sound channel, and generate noise.

To provide backwards compatibility with the ZX Spectrum, the SAM also provides a single-bit 'beeper' channel which can be used to emit simple tones by toggling the bit on and off as per the original Spectrum.

In order to match the processing speed of the ZX Spectrum (3.5MHz), the SAM Coupé introduces extra wait states in display mode 1 (the ZX Spectrum-compatible graphics mode) to slow down the CPU to roughly match the rate of that system.

SAM Coupé bootup screen

The machine shipped with 32 KB of ROM containing code to boot the machine and a BASIC interpreter (SAM BASIC) written by Andrew Wright and heavily influenced by his earlier Beta BASIC for the ZX Spectrum. The ROMs contained only the bootstrap code and the DOS was instead loaded from disk using the BOOT command, or the F9 key. The majority of disks shipped with SAMDOS, the system's first DOS, on them so that they could be directly booted. An improved replacement, MasterDOS, was also developed offering faster disk access, more files and support for the real-time clock accessory to provide file timestamps amongst many other improvements.

The BASIC was very advanced and included code for sprite drawing and basic vector shapes such as lines and circles. The screen co-ordinate system for these was variable and could be arbitrarily scaled and centered. A provision for "recording" sequences of graphics commands so that they could later be repeated without the speed penalty of a BASIC interpreter in between was provided.

The machine is capable of running CP/M 2.2 using the Pro-Dos software with support for both 720 Kilobyte format disks and IDE drives[3]

The original MGT SAM Coupé box — all original MGT material pictured a single disk drive inserted into the right hand side even though the machine required single drive users to use the left hand bay.

The SAM originally used Citizen 3.5 inch slimline drives which slotted in below the keyboard to provide front-facing slots. Like IDE hard disks, these enclosures contained not just the drives but also the drive controllers, a WD1772-02, with the effect that the SAM could use both drives simultaneously.

Due to a flaw in the Coupé's design, resetting the machine while a disk was left in a drive would be liable to cause data corruption on that disk, as while RESET is held in, no 8Mhz clock signal is sent to the drive's controllers. With the appropriate technical expertise, this fault was easily corrected.[4]

The double density disks used a format of 2 sides, 80 tracks per side and 10 sectors per track, with 512 bytes per sector. This gave a total capacity of 800 KB, though the standard directory occupied 20 KB leaving 780 KB free for user files. Files were stored in the same structure as MGT's original +D interface, but with additional codes used for SAM Coupé file types. The disk encoding (NRZ), encoding strategy (linear angular velocity), and track and sector header formats were compatible with those used on the IBM PC and Atari ST, and programs were available to read FAT formatted disks.

Rear view of the SAM Coupé. From left to right: NMI break button, MIDI IN/OUT ports, joystick port, mouse port, reset button, Euroconnector expansion port, cassette jack, stereo sound output/lightpen input, power button, SCART socket, power/RF socket

A large array of expansion ports were provided, including:

• Two internal drive bays.
• Non-standard SCART connector offering composite video and digital and linear RGB as well as power input.
• 64-pin Euroconnector for general purpose hardware expansions.
• Mouse socket (proprietary format, although a converter for Atari ST style mice was later available).
• Light pen / Light gun and Stereo sound output via 5-pin DIN connector.
• MIDI IN/OUT ports (and THROUGH, via a software switch).
• Network using the MIDI port (up to 16 machines could be interconnected).
• Atari-style 9-pin joystick port (dual capability with a splitter cable although due to a flaw the two joysticks would interfere with each other).
• 3.5 mm mono Cassette jack (dual use for loading and saving).

Up to four devices could be connected to the Coupé's Euroconnector port, through the use of the SAMBUS, which also provided a built-in clock. When using more power-hungry peripherals, the SAMBUS required an additional power supply.

The SAM's Power Supply was a modified Amstrad CPC MP1/MP2 modulator unit, with the RF modulator built in and connected via a joint power/TV socket to the computer. This made signal interference from the AC/DC converter common and it was a popular but entirely unofficial modification to remove the modulator and keep it as a separate unit.[5]

The Kaleidoscope, an extension of the Hardware Development Kit[8] was announced by SAMCo shortly before bankruptcy, extended the machine's total colour palette to 32,768 colours in such a way as to allow forwards and backwards compatibility by applications. Although complete, very few were produced and the design ceased with SAMCo.

Developed by Colin Piggot in 2007, this interface provides functions, being an Ethernet port running TCP/IP, an SD card slot supporting MMC, SD and SDHC cards up to 64GB for use with B-DOS and a 128 KByte EEPROM for interface and other settings storage. From B-DOS version 1.5t beta 6 and later a modified ROM is available to bootstrap the DOS from the EEPROM without the need to load from the floppy drive.[9]

MGT, Miles Gordon Technology, plc., which originally produced add-ons for the ZX Spectrum, launched the SAM Coupé late in 1989, missing the Christmas sales. They ended up with a vast number of machines in stock. The 16-bit and PC markets were on the rise and it helped little that MGT in the beginning of 1990 had to ship a new ROM to about 8,000 existing customers to fix bugs, notably a DOS booting bug. MGT went into receivership in June 1990.

Immediately after the collapse of MGT, the founders of the company, Alan Miles and Bruce Gordon, bought back the company's assets and formed SAM Computers Ltd. The price of the SAM with floppy disk drive was brought down to under £200 and new games and hardware were released. SAMCo survived until 15 July 1992.

Stock from SAM Computers Ltd. were bought by West Coast Computers in November 1992. They revamped the SAM Coupés and marketed them under the new name SAM Élite. The only changes made were that 512 KB became standard and an external printer connector was added.[11] The slim-line floppy drives from Citizen, who had withdrawn them from the European market in 1990, were replaced with standard 3.5 inch drives. Little is known about the company, other than that it was based in Gloucester and closed in August 1994,[12] presumably after the last of the SAMCo stock had sold. No new computers made by West Coast are known and this was likely the full extent of their business. For a long period the only point of contact was Format Publications, run by Bob Brenchley, which faded out of existence sometime around 1998.

In 2017, Andrews UK Limited registered "Sam Coupe" as a UK trademark, as well as the updated Sam Coupé logo.[13]

Flash!, an art package, was the only full application bundled with every SAM Coupé. Written by Bo Jangeborg, author of the earlier ZX Spectrum program The Artist and The Artist II, it offered pixel editing in all four graphics modes, conversion of graphics from one mode to another and some basic animation functions.

Only full screen images were supported and the program's main flaw was an inability to view the entirety of an image while working on it. A copy adapted for use with a mouse was bundled with the official mouse addon.

Screenshot of Sphera, a mode 2 vertically scrolling shooter.

An early supporter of the SAM, Enigma published SAM versions of Defenders of the Earth, Escape From the Planet of the Robot Monsters, Five on a Treasure Island (based on Enid Blyton's Famous Five), Klax, Pipe Mania and SAM originals SAM Strikes Out (a Jet Set Willy influenced platformer), Futureball (a Speedball influenced futuristic sporting title) and Sphera.

The software arm of SAMCo, founded in 1992 due to the lack of support from mainstream publishing houses, was notable for publishing most of the SAM's best titles. SAM original titles included Astroball, Batz 'n' Balls, Legend of Eshan and Wop Gamma. Revelation also published Hexagonia, which is similar to Atomix.

SAM ports included Elite (nothing more than the ZX Spectrum 48K version repackaged onto floppy disk), Prince of Persia, Manic Miner, Lemmings, Sophistry and Splat!.

A later incarnation of Revelation was set up in conjunction with West Coast Computers, with titles distributed by Format Publications.

Spun off from the disk based magazine, FRED Publishing was relatively late to the scene, but supported the machine long after any of the other publishing houses. The jewel in its crown was the SAM conversion of Lemmings (and Oh No! More Lemmings), but they also published a number of SAM original titles such as Boing, The Bulgulators, Dyzonium, Football League Manager, Impatience/Triltex, Momentum, Parallax, Waterworks and Witching Hour.

This label released titles such as Manic Miner and Dyadic. They also distributed titles for other authors, such as MasterBasic and MasterDos. The same team was also involved with the SAM Prime magazine.

A relatively late comer to the SAM scene, founded in 1995. Launching with a new soundcard for the SAM and continued producing a disk magazine to support it but later spanned over into games including Stratosphere and the Money Bags trilogy. Still actively producing software, hardware and a regular magazine for the SAM Coupe.

The primary community site is the Wiki https://www.worldofsam.org containing information, a forum and software repository containing many commercial titles released into the public domain.

Community sites also exist on Social Media with the most popular (as of March 2019) being the Sam Coupé Users Group on Facebook.

As a result of the low sales volume and high proliferation of disk based magazines, a number of individuals became well known amongst the SAM community. These include:

• George Boyle — Later editor of FRED
• Robert Brenchley — Editor of the long-running Sinclair and SAM Coupé print fanzine Format, and later built and distributed SAM Coupé 'Elite' models under the company name West Coast Computers.
• Graham Burtenshaw — author of SAM Paint and Momentum. Founder and editor of Enceladus magazine.
• Simon Cooke — Founder of the Entropy demo group, and contributor to Prince of Persia, Lemmings, Parallax, E-Tracker, FRED magazine and more. Was later a columnist for Your Sinclair magazine, writing the Spec Tec Jr column which covered readers' SAM Coupé and Sinclair Spectrum technical questions.
• František Fuka — programmer and musician.
• David Gommeren — author of the SAM games Tetris and Batz 'n Balls, and some demos.
• Neil Holmes and Stuart Leonardi - Creators of the games Parallax and Exodus, and demos under the name Masters of Magic.
• Colin Jordan — author of "'Five On a Treasure Island", "Splat" & the "SAM Adventure System (SAS)'". Also worked at SAMCo.
• Balor Knight — author of Astroball and Dyzonium.
• David Ledbury - Editor and creator of the magazine ZAT and SAM Prime.
• Colin MacDonald — original editor of FRED and man behind FRED Publishing.
• Malcolm Mackenzie — Persona Software. Publisher of Blitz Disk Based Magazine.
• Simon Owen — primary author of SimCoupe, the SAM Coupé emulator. Also creator of a Pacman clone, and debugger for the system.
• Colin Piggot — runs the company Quazar, which has been continuously producing hardware and software projects for the SAM Coupé for over two decades, including printed magazines, software disks, and hardware upgrades and replacements.
• Chris Pile — author of Pro-Dos (a CP/M implementation for SAM) and the port of Defender.
• Nick Roberts — programmer, responsible for the monthly SAM Coupé coverage in CRASH! and later PR Manager for SAMCo Ltd.
• Allan Skillman — author of XCoupe, the first emulator for the SAM Coupé, which was the prelude to SimCoupe.
• Brent Stevens — organiser of the SAM Coupé Public Domain Software Association. Also wrote SAM games and hardware reviews, and did related photography in Sinclair User magazine under the alias of Steve Brentwood.
• Ron Stirling — creator of Review disk magazine and MegaDisk compilation of games for SAMCo.
• Christopher J. White — game developer who created the SAM Coupé ports of Prince of Persia and Lemmings, publishing them under the Noesis label.
• Dave Whitmore — Technical Editor of the SAM Coupe Adventure Club, and later Sysop of Dalmation BBS in the mid-nineties, a dial-up BBS aimed at the SAM community.

The SAM Coupe had a number of publications created for it, mostly "fanzines" by Community members. Some of the more noted are listed below:

• Based On An Idea — paper-based magazine. Published by Simon Cooke and Martin Rookyard.
• Blitz — disk based magazine from the creators of SAM Newsdisk, SAM Prime and ZAT. Published by Persona.
• Enceladus — disk-based magazine published (and programmed) by Graham Burtenshaw.
• FRED — disk-based magazine published by Colin MacDonald (FRED 82 published by George Boyle)
• Format — paper-based magazine published by Robert Brenchley. (ISSN)0963-8598
• SAM Adventure Club — disk based magazine. Published by the SAM Coupe Adventure Club.
• SAM Newsdisk — official disk-based magazine published by SAM Computers Ltd by members of the "ZAT" and "SAM Quartet" teams.
• SAM Prime — disk (later paper) based magazine published by former SAM Newsdisk team members after SAMCo's demise.
• SAM Revival — paper-based magazine, with cover CD/disk. Currently the only remaining magazine under publication.
• SAM Supplement — disk based magazine published by Dave Tonks.
• ZAT — paper-based magazine for ZX Spectrum and SAM Coupé.