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Z80 Datasheet(PDF) 94 Page - Zilog, Inc. |
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Z80 Datasheet(HTML) 94 Page - Zilog, Inc. |
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94 / 330 page ![]() <%27 2GTKRJGTCNU 7UGT /CPWCN UM008101-0601 Direct Memory Access Notes : * Address can increment (+) or decrement (-) from the programmed starting address (As), which is the first address for transfer purposes. ** Occurs only in 2-cycle (variable timing) simultaneous transfers when the Ready line is still active at the end of the N + 1 byte transfer. *** Simultaneous transfers cannot have both ports variable. This class of operation is programmed as a DMA search-only operation, with variable addresses ascribed to the programmed source port. What the DMA senses is the source port may be either the real source or destination, as determined by external hardware. See “The actual number of bytes transferred is one more than specified by the block length. * These entries are necessary only in the case of a fixed destination address.” on page 129. Table 11. Contents of Counters After DMA Stops Because of End-of-Block (Transfer Operations) Class Mode Programmed Block Length Bytes Transferred At Stop Byte Counter Source Port Address Counter* Destination Port Address Counter* Sequential Byte N N+1 N As ±(N+1) As ±(N) Transfer Burst N N+1 N As ±(N+1) As ±(N) Continuous N N+1 N As ±(N+1) As ±(N) Search Only or Simultaneous Transfer/Search Byte N N+1 N As ±(N+1) *** Burst N N+1 N+1 As ±(N+1) *** Burst N N+2** N+1 ** As ±(N+2)** *** Continuous N+1 N+1 N+1 As ±(N+1) *** Continuous N+1 N+2** N+1 ** As ±(N+2)** *** Table 12. Contents of Counters After DMA Stops Due to Byte Match (Search or Transfer/ Search Operations) Class Mode Match Occurs On This Byte Bytes Transferred At Stop If Transferring Byte Counter Source Port Address Counter* Destination Port Address Counter Sequential Transfer Byte M M M-1 As ±(M) As ±(M-1) Burst M M M-1 As ±(M) As ±(M-) Continuous M M+ M-1 As ±(M) As ±(M -) Search Only or Simultaneous Transfer Search Byte MM MAs ±(M) *** Burst M M+1 M+1 As ±(M+1) *** Burst M M** M-1** As ±(M** *** Continuous M M+1 M+1 As ±(M+1) *** |
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