SS-50 Bus
Encyclopedia
The SS-50 bus was an early computer bus
designed as a part of the SWTPC 6800 Computer System that used the Motorola 6800
CPU. The SS-50 motherboard
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 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.
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 boards that did not need gold plated edge connector
s. The tin plated Molex connectors were only rated for a few insertions and were sometimes a problem in hobbyist systems were 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.
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
designed as a part of the SWTPC 6800 Computer System that used the Motorola 6800
Motorola 6800
The 6800 was an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System that also included serial and parallel interface ICs, RAM, ROM and other support chips...
CPU. The SS-50 motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
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
SWTPC
The U.S. company SWTPC started in 1964 as DEMCO . It was incorporated in 1967 as Southwest Technical Products Corporation of San Antonio, Texas...
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 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
Motorola 6809
The Motorola 6809 is an 8-bit microprocessor CPU from Motorola, designed by Terry Ritter and Joel Boney and introduced 1978...
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.
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 boards that did not need gold plated edge connector
Edge connector
An edge connector is the portion of a printed circuit board consisting of traces leading to the edge of the board that are intended to plug into a matching socket. The edge connector is a money-saving device because it only requires a single discrete female connector , and they also tend to be...
s. The tin plated Molex connectors were only rated for a few insertions and were sometimes a problem in hobbyist systems were 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.