IA186EM/IA188EM
Data Sheet
8-Bit/16-Bit Microcontrollers
February 25, 2011
Bit [5]—P → Relative Priority. When set to 1, selects high priority for this channel
relative to the other channel during simultaneous transfers.
Bit [4]—TDRQ → Timer 2 Synchronization. When set to 1, enables DMA requests from
Timer 2. When 0, disables them.
Bit [3]—Reserved.
Bit [2]—CHG → Change Start Bit. This bit must be set to 1 to allow modification of the
ST bit during a write. During a write, when CHG is set to 0, ST is not changed when
writing the control word. The result of reading this bit is always 0.
Bit [1]—ST → Start/Stop DMA Channel. When set to 1, the DMA channel is started.
The CHG bit must be set to 1 for this bit to be modified and only during the same register
write. A processor reset causes this bit to be set to 0.
Bit [0]—Bn/W → Byte/Word Select. When set to 1, word transfers are selected.
When 0, byte transfers are selected.
Note: Word transfers are not supported if the chip selects are programmed
for 8-bit transfers. The IA188EM does not support word transfers
5.1.9 D1TC (0d8h) and D0TC (0c8h)
DMA Transfer Count Registers. The DMA Transfer Count registers are maintained by each
DMA channel. They are decremented after each DMA cycle. The state of the TC bit in the
DMA control register has no influence on this activity. But, if unsynchronized transfers are
programmed or if the TC bit in the DMA control word is set, DMA activity ceases when the
transfer count register reaches 0. The D0TC and D1TC registers are undefined at reset (see
Table 25).
Table 25. DMA Transfer Count Registers
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
TC15–TC0
Bits [15–0]—TC15–TC0 → DMA Transfer Count contains the transfer count for the
respective DMA channel. Its value is decremented after each transfer.
5.1.10 D1DSTH (0d6h) and D0DSTH (0c6h)
The DMA DeSTination Address High Register. The 20-bit destination address consists of these
4 bits combined with the 16 bits of the respective Destination Address Low Register. A DMA
transfer requires that two complete 16-bit registers (high and low registers) be used for both the
source and destination addresses of each DMA channel involved. These four registers must be
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