Peripheral Interface: Difference between revisions
→The PI Bus
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The PI bus is the bus where external devices can be connected, via either the cartridge port on the top of the console, or the expansion port at the bottom of the console. Notice both ports are electrically connected to the same bus, even if the connector is different.
The bus address is 32-bit and the values being transferred are 16-bits. So each access (read or write) is made to a 32-bit address with a 16-bit data. The PI (as master device) issues reads and writes to the bus with a wire protocol detailed below. Each device is expected to use an address range (a subset of the whole 32-bit address space); the device will receive all reads and writes requests from PI, and is expected to reply / execute those falling within the address range of interest
The PI will issue reads or writes as drive by the CPU via two different systems:
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