38 lines
1.4 KiB
Markdown
38 lines
1.4 KiB
Markdown
# "BBU" Apple Custom Silicon
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The "BBU", as it is called on the Macintosh SE's printed circuit board
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silkscreen, is a relatively complex Apple custom silicon chip,
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compared to the other custom chips on the Macintosh SE's Main Logic
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Board (MLB). Despite its intimidating look as a chip with a huge
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number of pins, its purpose can be summarized as follows.
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* Provide a single address bus interface to ROM, RAM, and I/O devices,
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including simple digital I/O pins.
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* Scan the CRT by driving the primary digital control signals
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(`*VSYNC`, `*HSYNC`, `VIDOUT`).
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There might be additional processing functions it may provide as a
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convenience between the CPU and the various other hardware chips, but
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chances are these processing functions are relatively simple.
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Most of the I/O pins that are connected to the BBU are single-bit
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digital I/O signals that are relatively easy to understand. Reverse
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engineering the Macintosh SE's firmware may be required to determine
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how these pins are mapped into the CPU's address space, but once that
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determination is made, providing a replica interface to most of the
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connected hardware should be super-easy.
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The following I/O chips are connected to the BBU:
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* VIA interrupt controller
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* IWM/SWIM floppy disk controller
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* SCSI Controller
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* Serial Communications Controller (SCC)
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Other chips that are connected to the BBU are mainly interfaced via
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only simple, single-pin interfaces.
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