This group of signals is responsible for the control of operations between expansion slots. Slave (/SLAVEn) Each slot has its own /SLAVEn output, driven actively, all of which go into the collision detect circuitry. The "n" refers to the expansion slot number of the particular /SLAVE signal. Whenever a Zorro III PIC is responding to an address on the bus, it must assert its /SLAVEn output very quickly. If more than one /SLAVEn output occurs for the same address, or if a PIC asserts its /SLAVEn output for an address reserved by the local bus, a collision is registered and the bus controller asserts /BERR . The bus controller will assert /SLAVEn back to the interrupting device selected during a Quick Interrupt cycle , so any device supporting Quick Interrupts must be capable of tri-stating its /SLAVEn; all others can drive SLAVEn with a normal active output. Configuration Chain (/CFGINn, /CFGOUTn) The slot configuration mechanism uses the bus signals /CFGOUTn and /CFGINn, where "n" refers to the slot number. Each slot has its own version of both signals, which make up the configuration chain between slots. Each subsequent /CFGINn is a result of all previous /CFGOUTs, going from slot 0 to the last slot on the expansion bus. During the autoconfiguration process, an unconfigured Zorro III PIC responds to the 64K address space starting at either $00E80000 or $FF000000 if its /CFGINN signal is asserted. All unconfigured PICs start up with /CFGOUTn negated. When configured, or told to "shut up" a PIC will assert its /CFGOUTn, which results in the /CFGINn of the next slot being asserted. Backplane logic automatically passes on the state of the previous /CFGOUTn to the next /CFGINn for any slot not occupied by a PIC, so there's no need to sequentially populate the expansion bus slots. Backplane Type Sense (SenseZ3) This line can be used by the PIC to determine the backplane type. It is grounded on a Zorro II backplane, but floating on a Zorro III backplane. The Zorro III PIC connects this signal to a 1K pullup resistor to generate a real logic level for this line. It's possible, though more complicated, to build a Zorro III PIC that can actually run in Zorro II mode when in a Zorro II backplane. It's hardly necessary or required to support this backward compatibility mechanism, and in many cases it will be impractical. The Zorro III specification does require that this signal be used, at least, to shut the card down and pass /CFGIN to /CFGOUT when in a Zorro II backplane.
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