The SS-50 bus was an early

computer bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

designed as a part of the

SWTPC 6800 The SWTPC 6800 Computer System, simply referred to as SWTPC 6800, is an early microcomputer developed by the Southwest Technical Products Corporation and introduced in 1975. It was built around the Motorola 6800 microprocessor, from which it gets ...

Computer System that used the

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System (later dubbed ''68xx'') that also included serial and parall ...

CPU. The SS-50

motherboard A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see #Nomenclature, "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It ho ...

would have around seven 50-pin connectors for CPU and memory boards plus eight 30-pin connectors for I/O boards. The I/O section was sometimes called the SS-30 bus. Southwest Technical Products Corporation introduced this bus in November 1975 and soon other companies were selling add-in boards. Some of the early boards were floppy disk systems from Midwest Scientific Instruments, Smoke Signal Broadcasting, and Percom Data; an

EPROM An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) integrated circuit, chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored d ...

programmer from the Micro Works; video display boards from Gimix; memory boards from Seals. By 1978 there were a dozen SS-50 board suppliers and several compatible SS-50 computers. In 1979 SWTPC modified the SS-50 bus to support the new Motorola MC6809 processor. These changes were compatible with most existing boards and this upgrade gave the SS-50 Bus a long life. SS-50 based computers were made until the late 1980s. The SS-50C bus, the S/09 version of the SS-50 bus, extended the address by four

address line In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

s to 20 address lines to allow up to a

megabyte The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix ''mega'' is a multiplier of (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes ...

of memory in a system. Boards for the SS-50 bus were typically 9 inches wide and 5.5 inches high. The board had Molex 0.156 inch connectors while the motherboard had the pins. This arrangement made for low cost printed

circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a laminated sandwich structure of conductive and insulating layers, each with a pattern of traces, planes and other features (similar to wires on a flat surface) ...

s that did not need gold plated

edge connector An edge connector is the portion of a printed circuit board (PCB) consisting of signal trace, traces leading to the edge of the board that are intended to plug into a matching jack (connector), socket. The edge connector is a money-saving devic ...

s. The tin plated Molex connectors were only rated for a few insertions and were sometimes a problem in hobbyist systems where the boards were being swapped often. Later systems would often come with gold plated Molex connectors. The SS-30 I/O Bus had the address decoding on the motherboard. Each slot was allocated 4 address (the later MC6809 version upped this to 16 address.) This made for very simple I/O boards, the Motorola peripheral chips connected directly to this bus. Cards designed using the SS-30 bus often had their external connectors mounted such that they were accessible outside the computer chassis when installed in SWTPC motherboards.

SS-50 and SS-30 gallery

Click the images to enlarge. Image:SWTPC6800_open.jpg,

microcomputer system Image:SS50_BUS.jpg, SWTPC SS-50 Bus Image:SS30_BUS.jpg, SWTPC SS-30 I/O Bus

References

Computer buses *SS-50 {{Computer bus