Z80 Datasheet, PDF (180/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

< %27 2GTKRJGTCNU
7UGT /CPWCN

Bus Release on Match
When the DMA is programmed to stop (release the bus) on match in Burst
or Continuous modes, a match causes BUSREQ to go inactive on the next
DMA operation, for example, at the end of the next read in search-only,
simultaneous transfer/searches, or at the end of the following write in
sequential transfer or transfer/searches (Figure 68).
CLK
Active
RDY _Inactive
BUSREQ
Byte n
Read in
Byte n+1
Read in
and
Match Found
on Byte n
DMA
Inactive
Figure 68. Bus Release on Match (Burst and Continuous Modes)
Because of the pipelining scheme, matches are determined while the next
DMA read or write is being performed. Table 12 lists the number of bytes
transferred in any class or mode.
The RDY line can go inactive after the matching operation begins without
affecting this bus-release timing. However, the time at which RDY goes
inactive can affect the number of bytes transferred, as described in Table 11
and Figure 32.
Bus Release on Not Ready
Burst mode, when RDY goes inactive, causes BUSREQ to go High on the
next rising edge of CLK after the completion of its current byte operation,
for example, at the end of the current read in search-only, simultaneous
transfer/search, or at the end of the following write in sequential transfer/
UM008101-0601
Direct Memory Access