In September 1987 Computer and Video Games told British readers that Sega’s new console was “reminiscent of a 1950s conception of a futuristic toaster”. It was the Master System, and Mastertronic, a company best known for cheap computer games on cassette, was selling it in Britain for £99.95. In Japan and North America the machine lost badly to Nintendo. In Europe and Brazil it did well enough that Sega was still selling it there after its 16-bit successor had arrived.
The hardware inside came from a line of Sega consoles that began with the SG-1000 in 1983. Sega’s own manual calls its video chip an enhanced version of the Texas Instruments TMS9918A, whose family of chips drove the SG-1000 and MSX computers. What Sega added to that chip decided how Master System games look, and how they flicker.
Fast facts
- Maker: Sega.
- Released: October 1985 in Japan as the Mark III; 1986 in North America as the Master System; 1987 in Britain.
- UK price: £99.95 in 1987, with a Light Phaser gun and two games in one cartridge in the box.
- CPU: Zilog Z80A at 3.58 MHz.
- Memory: 8K of RAM for programs; 16K of video RAM on the video chip, out of the Z80’s reach.
- Video: Sega’s own VDP (video display processor): 256×192 pixels, 16 colours per tile from a palette of 64, 64 sprites, eight on a line.
- Sound: a programmable sound generator with three tone channels and one noise channel (a Texas Instruments SN76489 design).
- Games: cartridges, and credit-card-sized Sega Cards in a second slot.
From SG-1000 to Master System
Sega released its first home console, the SG-1000, in 1983. It used a Z80 at 3.58 MHz, a Texas Instruments TMS9928A video chip and a TI SN76489 sound chip. According to the 2019 book SEGA Master System: a visual compendium, the SG-1000 fell behind Nintendo’s Famicom, and Sega’s answer arrived in 1985 as the Mark III, named as its third console. The Mark III still played SG-1000 cartridges and the cheaper Sega Cards. The compendium reports that it sold a million machines in its first year, but that Sega could not persuade the big Japanese publishers to support it. Only two third-party Mark III games came out.
For America Sega redesigned the case in black and red plastic (the Mark III had been white), called it the Master System and launched it in 1986 through the toy company Tonka. The compendium reports 125,000 Master Systems sold in North America by the end of 1986, against 1.1 million NES consoles, with only Activision and Parker Brothers publishing for it. When the Master System reached Japan in 1987 it had a Yamaha YM2413 FM sound chip built in. On the Mark III that chip had been an add-on, the FM Sound Unit, and it did not appear in the Western models.
The video chip
Sega’s Software Reference Manual for the Sega Mark III describes the VDP as “a Sega designed custom chip whose architecture resembles an enhanced TMS9918A”. The TMS9918A had a fixed set of 15 colours plus transparent and could show only four sprites on a line. Sega’s chip keeps the older chip’s display modes so that SG-1000 games still run, and adds a new mode that almost every Master System game uses. The manual describes the new mode:
| Screen | 256×192 pixels, as 32×24 tiles of 8×8 pixels |
| Tiles | 16 colours each, 4 bits per pixel, drawn from two banks of 16 in colour RAM |
| Palette | 64 colours: two bits each of red, green and blue |
| Sprites | 64, each 8×8 or 8×16 pixels, eight on a line |
| Scrolling | smooth scrolling in both directions, with a fixed strip for a score |
| Interrupts | at the end of the frame, and on a chosen raster line |
The palette is 32 bytes inside the chip. Each byte holds two bits of red, two of green and two of blue, so each channel has four brightness levels: off, one third, two thirds and full. Tiles can use either bank of 16 colours. Sprites and the border always use the second. A tile in the background map can also be flipped horizontally or vertically and drawn in front of sprites, which lets a game reuse graphics and hide a character behind scenery.
The sprite limit is the one players notice. “Up to eight sprites can occupy a single horizontal raster line,” the manual says, and a line “containing nine or more sprites is not displayed properly.” It is the same limit the NES has, and Master System games get round it the same way, with sprite flicker.
Scrolling came with help for the score display. Two bits in the first control register stop the top two rows of tiles from scrolling sideways, or the right-hand eight columns from scrolling up and down, so that, as the manual puts it, “the scores remain in place”. The raster line interrupt lets a program change the horizontal scroll or the colours partway down the screen. The manual’s own example is changing a colour after the beam has drawn the top half.
The chip also sets rules for the programmer. The Z80 reaches it only through two input/output ports, and the manual warns that the chip cannot accept data faster than every 16 T-states during vertical blanking or every 29 during the picture: “you should never issue two consecutive OUT or IN instructions to the VDP”. A game that writes to the screen as fast as the Z80 can go loses data.
Paging the cartridge
The Z80 can address only 64K, and by 1987 Master System cartridges held 128K or more. The console pages the cartridge through the top of the address space. RAM sits at $C000–$DFFF and appears again at $E000–$FFFF, and Sega’s manual reserves the last few bytes of that copy as control registers. A write to $FFFF selects which 16K bank of the cartridge appears at $8000–$BFFF. Later developer notes add $FFFD and $FFFE for the two lower slots, and $FFFC for switching battery-backed RAM into the cartridge’s address space.
The registers themselves cannot be read, but each write also lands in the RAM underneath. The manual explains that “the bank select register appears to be read/write, even though what is actually read is the RAM image of the register”. A program can find out which bank is paged in by reading the address it wrote to. It also means those bytes are not free for anything else, and the manual tells programmers to put the stack at $DFF8, below them.
One piece of the cartridge never moves. The developer notes explain that the bottom 1K of the address space always shows the first 1K of the cartridge, “to ensure that the reset and interrupt vectors are always available”. The Z80 jumps to $0038 on every interrupt and to $0066 when the player presses the console’s pause button, so that code has to be there whichever bank is paged in.
Europe and Brazil
Britain first heard about the console in October 1986, when C+VG reported that Sega was launching its Master System. The machine arrived in 1987. Sega’s September 1987 advertisements in C+VG offered the console, two control pads, the Light Phaser and the built-in games for £99.95, “Distributed in the UK by Mastertronic Ltd”. That November C+VG printed Sega’s release schedule, with most games at £14.95 and the 3-D glasses and adaptor at £49.95. The glasses plugged into the card slot and used liquid-crystal shutters to show each eye a different frame.
The compendium describes a bad start: stock reached many shops in Britain, France and Germany only on Boxing Day 1987, too late for Christmas, and Mastertronic was left in financial trouble. Virgin bought the company, and as Virgin Mastertronic it handled Sega’s European distribution from 1988 until Sega bought it in 1991 and renamed it Sega Europe. The same firm brought the Mega Drive to Britain in 1990.
By the compendium’s figures the Master System had sold 6.25 million consoles in Europe by 1993, more than the Mega Drive’s 5.73 million by the same point, and nearly seven million by the end of its life, about 1.5 million of them in Britain. A cheaper redesign, the Master System II, arrived in 1990 without the card slot, and later models had Alex Kidd in Miracle World or Sonic the Hedgehog built in. European publishers such as US Gold, Domark, Codemasters and Probe wrote for it, and Sega kept making games for Europe after releases had stopped in Japan and America.
In Brazil the toy company Tectoy launched the console under licence in 1989. The compendium reports that Sega hardware and software brought in Cz$40 million of Tectoy’s Cz$66 million revenue in the first year, and that more than 8 million Master System consoles had been sold in Brazil by 2016. Estimates of worldwide sales vary between sources, from about 13 million to about 20 million.
Sega’s own games
With little third-party support outside Europe, most Master System games came from Sega. Many were arcade conversions (Space Harrier, Out Run, After Burner, Shinobi, Wonder Boy), squeezed into cartridges of 1 or 2 megabits. Sega also wrote games for the console itself. Alex Kidd in Miracle World gave it a mascot, and Phantasy Star (1987) was a science-fiction role-playing game that started a long-running series.
Sources
- Sega, Software Reference Manual for the Sega Mark III (1986): p. 4 (Z80A at 3.58 MHz; NMI from the pause button at
$0066), p. 5 (interrupt mode 1 at$0038), p. 6 (the VDP “resembles an enhanced TMS9918A”; resolution, 64-colour palette, 16K video RAM), pp. 7–10 (tiles, flipping and priority, scroll inhibit bits, sprites, colour RAM format), p. 12 (VDP access timing), pp. 17–18 (scroll registers and raster line interrupt), pp. 19–21 (system RAM, stack at$DFF8, bank register at$FFFFand its RAM image), p. 27 (three tone generators and a noise generator), pp. 39–40 (developer’s notes:$FFFC–$FFFFand the fixed first 1K). - Steve Jarratt and Damien McFerran, SEGA Master System: a visual compendium (Bitmap Books, 2019): the SG-1000’s CPU and chips (including the SN76489); the Mark III’s 1985 release, SG-1000 compatibility, first-year sales and third-party support; the Master System’s design, Tonka and 1986 North American sales; the Japanese Master System’s FM chip; the European launch, Boxing Day delays and Virgin Mastertronic; the Master System II; European and Brazilian sales; the 3-D glasses.
- Computer and Video Games issue 60, October 1986, contents page: “Sega is launching its Master System”.
- Computer and Video Games issue 71, September 1987: “Games Machines” supplement (the “futuristic toaster”; contents of the box); Sega advertisement (£99.95; distributed by Mastertronic).
- Computer and Video Games issue 73, November 1987: “Sega release schedule to November 1987” (console £99.95, 3-D glasses and adaptor £49.95, games from £14.95).
- Texas Instruments, TMS9918A/TMS9928A/TMS9929A Video Display Processors Data Manual (November 1982), section 2: the fixed colour set and four sprites per line.
- Wikipedia, “Master System” (web, secondary): the Mark III’s release date of 20 October 1985 and a worldwide estimate of 13 million. https://en.wikipedia.org/wiki/Master_System