Selecting Byte Or Word Size Transfers - Intel 80C188EC User Manual

Register Name:
Register Mnemonic:
Register Function:
15
D D D
D D D
A A A
1 1 1
5 4 3
Bit
Mnemonic
DDA15:0 DMA
Destination
Address
Figure 10-12. 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 10-13) 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.
DMA Destination Address Pointer (Low)
DxDSTL
Contains the lower 16 bits of the DMA Destination
pointer.
D D D D D
D D D D D
A A A
A A
1 1 1 9 8
2 1 0
Reset
Bit Name
State
XXXXH
DIRECT MEMORY ACCESS UNIT
D D D D D
D D D D D
A A A A
7 6 5 4
Function
DDA15:0 are driven on the lower 16 bits of the
address bus during the deposit phase of a DMA
transfer.
0
D D D
D D D
A A A A
3 2 1 0
A1179-0A
10-19