View source for SS-50 bus

{{Short description|Computer bus for 8-bit systems}}
{{Infobox computer hardware bus
| name        = SS-50 bus
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| image       = SS50_BUS.jpg
| alt         = SWTPC SS-50 Bus
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| invent-date = {{Start date and age|1975|11}}
| invent-name = [[SWTPC|Southwest Technical Products Corporation]]
| super-name  =
| super-date  =
| replaces    =
| width       =
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| speed       =
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| external    =
}}
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.<ref>[https://books.google.com/books?id=Bik2nThZSYoC&dq=Southwest+Technical+Products+Corporation+ss-50+bus+1975&pg=PA197 Is there a computer in the house?] By Guy Kewney, New Scientist, 19 Oct 1978, Page 197, ''...Other examples of non-standard "standard board" computers would include those based on South West Technical Products Corporation's SS50 bus, based in turn on...''</ref><ref>[https://books.google.com/books?id=Dj4EAAAAMBAJ&dq=68xx%27s+Family+is+Extended+ss-50&pg=PA46 68XX's Family is Extended], By Dale L. Puckett, InfoWorld, 13 Apr 1981, Page 46</ref> 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.
[[SWTPC|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|Midwest Scientific Instruments]], [[Smoke Signal Broadcasting]], and [[Percom|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.<ref>The S-100 and Other Micro Buses, Elmer C. Poe, James C. Goodwin</ref>
In 1979 SWTPC modified the SS-50 bus to support the new Motorola [[Motorola 6809|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]]s to 20 address lines to allow up to a [[megabyte]] of memory in a system.<ref>
[http://www.cs.unc.edu/~yakowenk/swtpc/ss50b.html "The S/09 version of the SS-50 and SS-30 busses"]
</ref><ref>
[http://www.swtpc.com/mholley/Tanner64K/64K_RAM_Index.htm "Digital Research / Tanner 64K SS-50C Memory Board"]
</ref>
Boards for the SS-50 bus were typically 9&nbsp;inches wide and 5.5&nbsp;inches high. The board had [[Molex]] 0.156&nbsp;inch connectors while the motherboard had the pins. This arrangement made for low cost printed [[circuit board]]s 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 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.<ref>{{cite web |url=http://www.corshamtech.com/ss-50-faqs/ |url-status=dead |archive-url=https://web.archive.org/web/20160123060653/http://www.corshamtech.com/ss-50-faqs/ |archive-date=2016-01-23 |title=SS-50 FAQs – Corsham Technologies, LLC}}</ref> 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.
<gallery>
Image:SWTPC6800_open.jpg|[[SWTPC 6800]] microcomputer system
Image:SS50_BUS.jpg|SWTPC SS-50 Bus
Image:SS30_BUS.jpg|SWTPC SS-30 I/O Bus
</gallery>
==References==
{{reflist}}
{{DEFAULTSORT:Ss-50 Bus}}
[[Category:Computer buses]]
[[Category:Early microcomputers|*SS-50]]
{{Computer bus}}