Z80 Datasheet, PDF (157/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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System Data Bus
47LS
245
DIR EN
On-Card Data Bus
DMA.CE
SIO.CE
PIO.CE
CTC.CE
RD
DMA.HAS.BUS
IORQ
M1
CARD.IEO
CARD.IEI
ON.CARD.ENABLE
DRIVE.DATA.OUT
ON.CARD.READ
DMA.WRITE
RD
ON.CARD.INT ACK
Figure 54. Data Bus Buffer Control Example
Z80 DMA and Z80 SIO Example
A common DMA application is performing data transfers over a serial data
link. The Z80 SIO peripheral is used to interface to the link, providing
conversion between serial and parallel data formats, synchronization, and
other functions.
Comparing the efficiency of interrupt driven and DMA data transfers
requires examination of the event sequences during the brief time intervals
in which the SIO needs a character (byte) transfer. Most of the time the SIO
is busy transmitting or receiving message bits and requires no service.
The SIO must be programmed to drive its WAIT/RDY line as a RDY signal
to the DMA, which is programmed for active-Low RDY in Byte mode.
UM008101-0601
Direct Memory Access