Intel 80C186XL, User Manual

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DIRECT MEMORY ACCESS UNIT
10-14
Figure 10-10. DMA Destination Pointer (Low-Order Bits)
10.2.1.2 Selecting Byte or Word Size Transfers
The WORD bit in the DMA Control Register (Figure 10-11) controls the data size for a channel.
When WORD is set, the channel transfers data in 16-bit words. Byte transfers are selected by
clearing the WORD bit. The data size for a channel also affects pointer indexing. Word transfers
modify (increment or decrement) the pointer registers by two for each transfer, while byte trans-
fers modify the pointer registers by one.
Register Name: DMA Destination Address Pointer (Low)
Register Mnemonic: DxDSTL
Register Function: Contains the lower 16 bits of the DMA Destination
pointer.
Bit
Mnemonic
Bit Name
Reset
State
Function
DDA15:0 DMA
Destination
Address XXXXH DDA15:0 are driven on the lower 16 bits of the
address bus during the deposit phase of a DMA
transfer.
15 0
D
D
A
1
D
D
A
2
D
D
A
3
D
D
A
0
D
D
A
5
D
D
A
6
D
D
A
7
D
D
A
4
D
D
A
9
D
D
A
1
0
D
D
A
1
1
D
D
A
8
D
D
A
1
3
D
D
A
1
4
D
D
A
1
5
D
D
A
1
2
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