DIRECT MEMORY ACCESS UNIT

Register Name:

DMA Control Register

Register Mnemonic:

DxCON

Register Function:

Controls DMA channel parameters.

15

D

D

D

S

M

D

I

M

E

E

N

E

M

C

C

M

 

 

 

 

SS D I E N C C

TI C N T

S

S

P

I

Y

Y

 

D

N

N

 

R

1

0

 

Q

 

 

 

 

 

 

 

0

 

C

S

W

 

H

T

O

 

G

R

R

 

 

T

D

 

 

 

 

A1180-0A

Bit

Bit Name

Reset

 

 

Function

Mnemonic

State

 

 

 

 

 

 

 

 

 

 

TC

Terminal

X

Set TC to terminate transfers on Terminal Count. This bit

 

Count

 

is ignored for unsynchronized transfers (that is, the DMA

 

 

 

channel behaves as if TC is set, regardless of its

 

 

 

condition).

 

 

 

 

 

INT

Interrupt

X

Set INT to generate an interrupt request on Terminal

 

 

 

Count. The TC bit must be set to generate an interrupt.

 

 

 

 

SYN1:0

Synchron-

XX

Selects channel synchronization:

 

ization Type

 

SYN1 SYN0

Synchronization Type

 

 

 

 

 

 

0

0

Unsynchronized

 

 

 

0

1

Source-synchronized

 

 

 

1

0

Destination-synchronized

 

 

 

1

1

Reserved (do not use)

 

 

 

 

P

Relative

X

Set P to select high priority for the channel; clear P to

 

Priority

 

select low priority for the channel.

 

 

 

 

IDRQ

Internal

X

Set IDRQ to select internal DMA requests and ignore

 

DMA

 

the external DRQ pin. Clear IDRQ to select the DRQ pin

 

Request

 

as the source of DMA requests. When IDRQ is set, the

 

Select

 

channel must be configured for source-synchronized

 

 

 

transfers (SYN1:0 = 01).

 

 

 

 

 

 

NOTE: Reserved register bits are shown with gray shading. Reserved bits must be written to a logic zero to ensure compatibility with future Intel products.

Figure 10-11. DMA Control Register (Continued)

10-16

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Image 271
Intel 80C186XL, 80C188XL user manual Synchronization Type, Idrq