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參數(shù)資料
| 型號： | HS9-82C37ARH-8 |
| 廠商： | Harris Corporation |
| 英文描述： | Radiation Hardened CMOS High Performance Programmable DMA Controller |
| 中文描述： | 輻射加固的CMOS高性能可編程DMA控制器 |
| 文件頁數(shù)： | 21/28頁 |
| 文件大小： | 253K |
| 代理商： | HS9-82C37ARH-8 |
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21
HS-82C37ARH
FIGURE 9. CASCADED HS-82C37ARHs
When programming cascaded controllers, start with the first
level (closest to the microprocessor). After RESET, the
DACK outputs are programmed to be active low and are
held in the high state. If they are used to drive HLDA directly,
the second level device(s) cannot be programmed until
DACK polarity is selected as active high on the initial device.
Also, the initial device’s mask bits function normally on cas-
caded channels, so they may be used to inhibit second-level
services.
Transfer Types
Each of the three active transfer modes can perform three
different types of transfers. These are Read, Write and Ver-
ify. Write transfers move data from an I/O device to the mem-
ory by activating MEMW and IOR. Read transfers move data
from memory to an I/O device by activating MEMR and IOW.
Verify transfers are pseudo-transfers. The HS-82C37ARH
operates as in Read or Write transfers generating addresses
and responding to EOP, etc., however the memory and I/O
control lines all remain inactive. Verify mode is not permitted
for Memory-to-Memory operation. Ready is ignored during
Verify transfers.
Autoinitialize
- By programming a bit in the Mode Register,
a channel may be set up as an Autoinitialize channel. During
Autoinitialization, the original values of the Current Address
and Current Word Count Registers are automatically
restored from the Base Address and Base Word Count Reg-
isters of that channel following EOP. The base registers are
loaded simultaneously with the current registers by the
microprocessor and remain unchanged throughout the DMA
service. The mask bit is not set when the channel is in Auto-
initialize. Following Autoinitialization, the channel is ready to
perform another DMA service, without CPU intervention, as
soon as a valid DREQ is detected, or software request made.
Memory-to-Memory
- To perform block moves of data from
one memory address space to another with minimum of pro-
HS-80C86RH
MICRO-
PROCESSOR
1ST LEVEL
HRQ
HLDA
DREQ
DACK
HS-82C37ARH
DREQ
DACK
INITIAL DEVICE
2ND LEVEL
HRQ
HLDA
HS-82C37ARH
HRQ
HLDA
HS-82C37ARH
ADDITIONAL
DEVICES
gram effort and time, the HS-82C37ARH includes a Mem-
ory-to-Memory transfer feature. Programming a bit in the
Command Register selects channels 0 and 1 to operate as
Memory-to-Memory transfer channels.
The transfer is initiated by setting the software or hardware
DREQ for channel 0. The HS-82C37ARH requests a DMA
service in the normal manner. After HLDA is true, the device,
using four-state transfers in Block Transfer Mode, reads data
from the memory. The channel 0 Current Address Register is
the source for the address used and is decremented or
incremented in the normal manner. The data byte read from
the memory is stored in the HS-82C37ARH internal Tempo-
rary Register. Another four-state transfer moves the data to
memory using the address in channel 1’s Current Address
Register and incrementing or decrementing it in the normal
manner. The channel 1 Current Word Count Register is dec-
remented.
When the word count of channel 1 goes to FFFFH, a TC is
generated causing an EOP output terminating the service.
Channel 0 word count decrementing to FFFFH will not set
the channel 0 TC bit in the Status Register or generate an
EOP in this mode. It will cause an Autoinitialization of chan-
nel 0, if that option has been selected.
If full Autoinitialization for a Memory-to-Memory operation is
desired, the channel 0 and channel 1 word counts must be
set equal before the transfer begins. Otherwise, if channel 0
underflows before channel 1, it will Autoinitialize and set the
data source address back to the beginning of the block. If
the channel 1 word count underflows before channel 0, the
Memory-to-Memory DMA service will terminate, and channel
1 will Autoinitialize but channel 0 will not.
In Memory-to-Memory Mode, Channel 0 may be pro-
grammed to retain the same address for all transfers. This
allows a single byte to be written to a block of memory. This
channel 0 address hold feature is selected by bit 1 in the
Command Register.
The HS-82C37ARH will respond to external EOP signals
during Memory-to-Memory transfers, but will only relinquish
the system busses after the transfer is complete (i.e., after
an S24 state). Data comparators in block search schemes
may use this input to terminate the service when a match is
found. The timing of Memory-to-Memory transfers is found in
Figure 5. Memory-to-Memory operations can be detected as
an active AEN with no DACK outputs.
Priority
- The HS-82C37ARH has two types of priority
encoding available as software selectable options. The first
is Fixed Priority which fixes the channels in priority order
based upon the descending value of their numbers. The
channel with the lowest priority is 3 followed by 2, 1 and the
highest priority channel, 0. After the recognition of any one
channel for service, the other channels are prevented from
interfering with the service until it is completed.
The second scheme is Rotating Priority. The last channel to
get service becomes the lowest priority channel with the oth-
ers rotating accordingly. The next lower channel from the
channel serviced has highest priority on the following
request: Priority rotates every time control of the system
busses is returned to the processor.
Spec Number
518058
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