Intel 80C186XL, User Manual

Page: 270 / 405

10-15
DIRECT MEMORY ACCESS UNIT
Figure 10-11. DMA Control Register
Register Name: DMA Control Register
Register Mnemonic: DxCON
Register Function: Controls DMA channel parameters.
Bit
Mnemonic
Bit Name
Reset
State
Function
DMEM Destination
Address
Space
Select X Selects memory or I/O space for the destination
pointer. Set DMEM to select memory space; clear
DMEM to select I/O space.
DDEC Destination
Decrement X Set DDEC to automatically decrement the destination
pointer after each transfer. (See Note.)
DINC Destination
Increment X Set DINC to automatically increment the destination
pointer after each transfer. (See Note.)
SMEM Source
Address
Space
Select X Selects memory or I/O space for the source pointer.
Set SMEM to select memory space; clear SMEM to
select I/O space.
SDEC Source
Decrement X Set SDEC to automatically decrement the source
pointer after each transfer. (See Note.)
SINC Source
Increment X Set SINC to automatically increment the source
pointer after each transfer. (See Note.)
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. A pointer remains constant if
its increment and decrement bits are equal.
15 0
S
T
R
T
C
H
G
W
O
R
D
P S
Y
N
0
S
Y
N
1
I
D
R
Q
T
C
S
I
N
C
S
D
E
C I
N
T
D
I
N
C
D
D
E
C D
M
E
M
S
M
E
M
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