Software Commands; Design Considerations; Programming Considerations; Dma Software Commands - Intel 386 User Manual

Intel386™ EX EMBEDDED MICROPROCESSOR USER'S MANUAL

12.3.16 Software Commands

The DMA contains four software commands: clear byte pointer, clear DMA, clear mask register,
and clear transfer complete signal. Each software command has an I/O address associated with it
(see Table 12-4). To issue a software command, write to its I/O address; the data written doesn't
matter —writing to the location is all that is necessary.
Name
(Address)
DMACLRBP Clear byte pointer
(0F00CH or
000CH)
DMACLR Clear DMA
(0F00DH or
000DH)
DMACLRMSK Clear mask register
(0F00EH or
000EH)
DMACLRTC Clear transfer complete signal
(0F01EH)

12.4 DESIGN CONSIDERATIONS

EOP# requires an external pull-up resistor. To determine the maximum value, the rise time must
be less than three bus cycles. To determine the minimum value, use the I
Intel386™ EX Embedded Microprocessor datasheet (order number 272420).

12.5 PROGRAMMING CONSIDERATIONS

Consider the following when programming the DMA.
•
The DMA transfers data between a requester and a target. The transfer direction is
programmable and determines whether the requester or the target is the source or
destination of a transfer.
•
The two-cycle data transfer bus cycle option uses a four-byte temporary buffer. During a
buffer transfer, the channel fills the temporary buffer from the source before writing any
data to the destination. Therefore, the number of bus cycles that it takes to transfer data
from the source to the destination depends on the amount of data to transfer and the source
and destination data bus widths.
•
Each channel contains a 26-bit requester address, 26-bit target address, and 24-bit byte
count. These values are programmed through the use of 8-bit registers, some of which are
multiplexed at the same addresses. A byte pointer (BP) controls the access to these
multiplexed registers. After you write or read a register that requires a byte pointer
specification, the channel toggles the byte pointer. For example, writing to DMA0TAR0
12-50
Table 12-4. DMA Software Commands
Command Functions
Resets the byte pointer flip-flop. Perform this
command at the beginning of any access to the
channel registers, to ensure a predictable place in
the register programming sequence.
Sets all DMA functions to their default states.
Simultaneously clears the mask bits of all channels
(enabling all channels).
Resets the transfer complete signal (DMAINT).
Allows the source of the DMA request (hardware or
software) to acknowledge the completion of a
transfer process.
OL
specification from the