CS82C37A datasheet(13/23 Pages) HARRIS

13 / 23 page

4-204

82C37A

Figure 7 shows an application for a DMA system using the

82C37A DMA controller and the 80C286 Microprocessor.

In this application, the system clock comes from the 82C284

clock generator PCLK signal which is inverted to provide

proper READY setup and hold times to the DMA controller in

an 80C286 system. The Read and Write signals from the

DMA controller may be wired directly to the Read/Write con-

trol signals from the 82C288 Bus Controller. The octal latch

for A8-A15 from the DMA controller’s data bus is on the local

80C286 address bus so that memory chip selects may still

be generated during DMA transfers. The transceiver on A0-

A7 is controlled by AEN and is not necessary, but may be

used to drive a heavily loaded system address bus during

transfers. The data bus transceivers simply isolate the DMA

controller from the local microprocessor bus and allow pro-

gramming on the upper or lower half of the data bus.

FIGURE 7. 80C286 DMA APPLICATION

MEMW

MEMR

MEMCS

MEMORY

A0 - A23

IOW

DACK

I/O

IOR

SYSTEM

BUS

TRANSCEIVER

T/R

DEVICE

DREQ

D0 - D15

TRANS-

CEIVER

TRANS-

CEIVER

LATCH

STB

AEN

D0-D7

VCC

A0-A7

IOR

IOW

MEMR

MEMW

DACK 0-3

D0-D7

DREQ 0-3

EOP

AEN

ADSTB

HRQ

HLDA

CLK

READY

82C37A

IOR

IOW

MEMR

MEMW

TO CORRESPONDING

82C288 SIGNALS AND

MEMORY/PERIPHERALS

TRANSCEIVER

LATCH

DECODE

CHIP SELECT

TO MEMORY/

PERIPHERALS

80C286

A0-A23

D0-D15

READY

HLD

HLDA

CLK

IORC

IOWC

MRDC

MWTC

IOR

IOW

MEMR

MEMW

CLK

82C288

82C284

CLK

PCLK

READY

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