參數(shù)資料
型號(hào)： A8237
廠商： Altera Corporation
英文描述： PROGRAMMABLE DMA CONTROLLER
中文描述： 可編程DMA控制器
文件頁(yè)數(shù)： 13/22頁(yè)
文件大?。?/td> 269K
代理商： A8237
Altera Corporation
17
a8237 Programmable DMA Controller Data Sheet
Clear Byte Pointer Command
The byte pointer is a single-bit internal register that selects either the least
significant or most significant byte of the 16-bit registers in the
a8237
. The
byte pointer allows microprocessor write and read operations via the 8-bit
data bus. The clear byte pointer command is a write command that resets
the byte pointer, allowing subsequent access to the least significant byte
of any 16-bit register. The data bus value for the clear byte pointer
command is ignored. The
reset
input and the master clear command
resets the byte pointer.
Set Byte Pointer Command
The
set byte pointer command is a read command that sets the byte
pointer, allowing subsequent access to the most significant byte of any
16-bit register. The data bus value for the set byte pointer command is
unknown. The byte pointer is reset by the
reset
input and the master
clear command.
Master Clear Command
The master clear command performs the same function as the
reset
input. This command resets the command, status, request, temporary and
byte pointer registers, mode register counter, state machine, and also sets
the mask register.
Clear Mask Register Command
The clear mask register
command is a write command that resets the 4-bit
mask register, enabling DMA requests from the
dreq
inputs. The data bus
value for the clear mask register
command is ignored.
Clear Mode Register Counter Command
The clear mode register counter command is a read command that resets
the 2-bit mode register counter. This counter is incremented after each
subsequent read of the mode register, allowing the user to cycle through
all four mode registers. The data bus value for the clear mode register
counter command is unknown.
Operation
This section describes the following
a8237
MegaCore function
operations:
I
I
I
State machine
Transfer modes
Other operations
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