Zilog Z08470 User Manual
Page 176
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UM008101-0601
Direct Memory Access
Figure 64.
Simultaneous Memory-to-I/O Transfer (Byte Mode)
Figure 63 illustrates the timing for simultaneous transfers in Burst and Con-
tinuous modes between memory and I/O, using standard Z80 timing. The
timing within each cycle is similar to the memory read cycle shown in
Figure 61. The address bus activity is the same, and the cycle length is the
same. However, the MREQ, RD, IORQ, and WR lines in Figure 61 have
been changed to MEMRD and IOWR lines in Figure 63. In addition, the
data bus becomes active earlier in Figure 63, in response to the MEMRD
line becoming active. Data is clocked to the l/O port on the rising edge of
IOWR
Figure 64 depicts the timing for Byte mode. Timing is identical to
Figure 63 within each cycle. The breaks between each cycle, where the
address and data bus are tristated and the MEMRD and IOWR lines remain
CE/WAIT
A15–A0
CLK
D7–D0
IOWR
MEMRD
Cycle 2
DMA Drives
the Last Data
it Read During
this Time
Cycle 1