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Yes, Intel had pointless restraints on pin counts; the 8008 processor was barely allowed 18 pins. So the 8080 designers were lucky that they got all the way to
by kens 3y ago
Yes, Intel had pointless restraints on pin counts; the 8008 processor was barely allowed 18 pins. So the 8080 designers were lucky that they got all the way to 40 pins. Federico Faggin has ranted about this in a few places.
As far as applications of the bus, multiprocessing was a big motivation. Intel had big plans with their Multibus. Intel had more plans for coprocessors as well. They introduced the 8089 I/O coprocessor to provide mainframe-style channel I/O, but it wasn't very popular.
- ggeorgovassilis 3y agoMore pins means more soldering when planting the chip on a mainboard (even if sockets are used, they need to be soldered, too) which increases time, cost and chances that something goes wrong and the entire mainboard must be discarded.
- monocasa 3y agoYeah, but that's a balance like everything else. It's far too easy to end up somewhere where the complete design requires added complexity to figure out the state of the multipurposed pins (and that associated logic's additional pin count) that you end up with a harder to manufacture product. Edit: adding that this is in the late 70s/early 80s where final integrators were using a bunch of 7000s-esque logic to glue the board together. Nowadays of course we can assume so many transistors on both sides of a trace that super generic sets of SERDES-style pairs makes sense nowadays for most complex buses.
- bogantech 3y agoThrough-hole components would be wave soldered not done by hand - so no, time and reliability have nothing to do with it. Just about any manufacturer would be reworking boards that failed QA not throwing them away.
- h2odragon 3y agohad to go refresh my memory on the 8089; here's a manual in case anyone else is curious. Its fun. http://bitsavers.org/pdf/intel/ISIS_II/9800938-01_8089_Assembler_Users_Guide_Aug79.pdf http://bitsavers.org/pdf/intel/ISIS_II/9800938-01_8089_Assem...
- chiph 3y agoIs the 8089 Intel's equivalent to Motorola's 6820 PIA? (I've never seen a 8089 in the wild - 6820s are often used in pinball machines)
- kens 3y agoNo, the Motorola 6820 simply provides two I/O ports. The Intel 8089 is a complete processor with its own instruction set, acting as an intelligent DMA controller. So you can run complex programs on the 8089 to process the I/O data. The model is kind of like the I/O channels in an IBM mainframe; you're offloading I/O tasks from the main processor to a special I/O processor.