The data time signals here manage the actual transfer of data between master and slave for both full and short cycle types. The burst mode signals are here too, as they're basically data phase signals even through they don't only concern the transfer of data. Data Output Enable (DOE) This signal is used by an expansion card to enable the buffers on the data bus. The bus master drives this line is to keep slave PICs from driving data on the bus until data time. Data Bus (D0-D31) This is the Zorro III data bus, which is driven by either the master or the slave when DOE is asserted by the master (based on READ ). It's valid for reads when /DTACK is asserted by the slave; on writes when at least one of /DSn is asserted by the master, for all cycle types. Data Strobes (/DSn) These strobes fall during data time; /DS3 strobes D24-D31, while /DS0 strobes D0-D7. For write cycles, these lines signal data valid on the bus. At all times, they indicate which bytes in the 32-bit data word the bus master is actually interested in. For cachable reads, all four bytes must be returned, regardless of the value of the sizing strobes. For writes, only those bytes corresponding to asserted /DSN are written. Only contiguous byte cycles are supported; e.g., /DS3-0 = 2, 4, 5, 6, or 10 is invalid. Data Transfer Acknowledge (/DTACK) This signal is used to normally terminate a Zorro III cycle. The slave is always responsible for driving this signal. For a read cycle, it asserts /DTACK as soon as it has driven valid data onto the data bus. For a write cycle, it asserts /DTACK as soon as it's done with the data. Latching the data on writes may be a good idea; that can allow a slave to end the cycle before it has actually finished writing the data to its local memory. Cache Inhibit (/CINH) This line is asserted at the same time as /SLAVEn to indicate to the bus master that the cycle must not be cached . If a device doesn't support caching, it must assert /CINH and actually obey the /DSn byte strobes for read cycles. Conversely, if the device supports caching, /CINH is negated and the device returns all four bytes valid on reads, regardless of the actual supplied /DSn strobes. Multiple Cycle Transfers (/MTCR, /MTACK) These lines comprise the Multiple Transfer Cycle handshake signals. The bus master asserts /MTCR at the start of data time if it's capable of supporting Multiple Transfer Cycles , and the slave asserts /MTACK with /SLAVEn if it's capable of supporting Multiple Transfer Cycles . If the handshake goes through, /MTCR strobes in the short address and write data as long as the full cycle continues.
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