Motorola DSP96002 User Manual page 136

Block transfer mode is selected. Clearing DE during DMA operation will stop the DMA only after the present
DMA transfer has been completed (the data is stored in the destination), setting DTD.
DE
0
1
7.5.4 DMA Counter (DCO)
The DMA Counter is a read/write 32-bit register that contains the number of DMA data transfers to be done.
If the DMA channel is set to Single Block transfer mode then, after each DMA data transfer, the DMA
Counter is decremented by one and tested for zero. When the count reaches zero, the DMA Block transfer
is done and the DMA channel will stop the data transfers. If the channel is set to Single Word mode (DTM1-
DTM0=11), the contents of the DMA counter are ignored since each DMA data transfer is done on demand.
The DMA Counter should not be written while the DMA channel is operating in one of the Block Transfer
modes. The DMA Counter may be written only when the channel is disabled (DE=0 and DTD=1), or when
in Single Word mode (DTM1-DTM0=11).
7.5.5 DMA Address Registers (DSR and DDR)
The DMA Source Address register (DSR) and the DMA Destination Address register (DDR) are two 32-bit
registers that contain the addresses of the source and destination, respectively, for the next DMA transfer.
The DMA Address registers are functionally identical to the Address Generation Unit address registers.
7.5.6 DMA Offset Registers (DSN and DDN)
The DMA Source Offset register (DSN) and the DMA Destination Offset register (DDN) are two 32-bit reg-
isters that specify the offset values used to update the respective DMA address registers. Each offset reg-
ister is read when the associated address register is read and used as input to its modulo arithmetic unit.
The DMA Offset registers are functionally identical to the Address Generation Unit offset registers.
7.5.7 DMA Modifier Registers (DSM and DDM)
The DMA Source Modifier register (DSM) and the DMA Destination Modifier register (DDM) are two 32-bit
registers that specify the type of arithmetic used to update the respective DMA address register during DMA
address register update calculations. Each modifier register is read when the associated address register
is read and used as input to its modulo arithmetic unit. The DMA Modifier registers are functionally identical
to the Address Generation Unit modifier registers. Both DMA modifier registers are set to $FFFFFFFF (lin-
ear arithmetic) during a processor reset or software reset.
7.5.8 DMA ALU
The ALU is common to the DMA and Address Generation Unit, and time multiplexed between them. The
DMA ALU is hardwired in the (R)+N configuration. Users can increment or decrement by 1 or N by loading
the DMA Offset registers accordingly. For example, DMA block transfers with DSP96002 word addressable
memory would often load the DMA Offset register with +1. However, interpolation, decimation, and commu-
tation operations could require an arbitrary address offset value N. DMA block transfers with byte address-
7 - 50
DMA Operation
Disabled
Enabled
DSP96002 USER'S MANUAL MOTOROLA