ADSP-21MOD870 데이터 시트보기 (PDF) - Analog Devices
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ADSP-21MOD870 Datasheet PDF : 32 Pages
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ADSP-21mod870
Unused bits in the 8-bit data memory formats are filled with 0s.
The BIAD register field is used to specify the starting address
for the on-chip memory involved with the transfer. The 14-bit
BEAD register specifies the starting address for the external byte
memory space. The 8-bit BMPAGE register specifies the start-
ing page for the external byte memory space. The BDIR register
field selects the direction of the transfer. Finally the, 14-bit
BWCOUNT register specifies the number of DSP words to
transfer and initiates the BDMA circuit transfers.
Table VI. Data Formats
BTYPE
00
01
10
11
Internal
Memory Space
Program Memory
Data Memory
Data Memory
Data Memory
Word Size
24
16
8
8
Alignment
Full Word
Full Word
MSBs
LSBs
BDMA accesses can cross page boundaries during sequential
addressing. A BDMA interrupt is generated on the completion
of the number of transfers specified by the BWCOUNT register.
The BWCOUNT register is updated after each transfer so it can
be used to check the status of the transfers. When it reaches zero,
the transfers have finished and a BDMA interrupt is generated.
The BMPAGE and BEAD registers must not be accessed by the
processor during BDMA operations.
The source or destination of a BDMA transfer will always be
on-chip program or data memory.
When the BWCOUNT register is written with a nonzero value,
the BDMA circuit starts executing byte memory accesses with
wait states set by BMWAIT. These accesses continue until the
count reaches zero. When enough accesses have occurred to
create a destination word, it is transferred to or from on-chip
memory. The transfer takes one processor cycle. Processor
accesses to external memory have priority over BDMA byte
memory accesses.
The BDMA Context Reset bit (BCR) controls whether the
processor is held off while the BDMA accesses are occurring.
Setting the BCR bit to 0 allows the processor to continue opera-
tions. Setting the BCR bit to 1 causes the processor to stop
execution while the BDMA accesses are occurring, to clear the
context of the processor, and start execution at address 0 when
the BDMA accesses have completed. The BDMA overlay bits
specify the OVLAY memory blocks to be accessed for internal
memory.
Internal Memory DMA Port (IDMA Port; Host Memory
Mode)
The IDMA Port provides an efficient means of communication
between a host system and the ADSP-21mod870. The port is
used to access the on-chip program memory and data memory
of the processor with only one processor cycle per word over-
head. The IDMA port cannot be used, however, to write to the
processor’s memory-mapped control registers. A typical IDMA
transfer process is described as follows:
1. Host starts IDMA transfer.
2. Host checks IACK control line to see if the processor is busy.
3. Host uses IS and IAL control lines to latch either the DMA
starting address (IDMAA) or the PM/DM OVLAY selection
into the processor’s IDMA control registers.
If IAD[15] = 1, the value of IAD[7:0] represents the IDMA
overlay: Bits 14:8 must be set to 0.
If IAD[15] = 0, the value of IAD[13:0] represents the start-
ing address of internal memory to be accessed and IAD[14]
reflects PM or DM for access.
4. Host uses IS and IRD (or IWR) to read (or write) processor
internal memory (PM or DM).
5. Host checks IACK line to see if the processor has completed
the previous IDMA operation.
6. Host ends IDMA transfer.
The IDMA port has a 16-bit multiplexed address and data bus
and supports 24-bit program memory. The IDMA port is com-
pletely asynchronous and can be written to while the ADSP-
21mod870 is operating at full speed.
The processor memory address is latched and is then automati-
cally incremented after each IDMA transaction. An external
device can therefore access a block of sequentially addressed
memory by specifying only the starting address of the block.
This increases throughput as the address does not have to be
sent for each memory access.
IDMA Port access occurs in two phases. The first is the IDMA
Address Latch cycle. When the acknowledge is asserted, a 14-bit
address and 1-bit destination type can be driven onto the bus by
an external device. The address specifies an on-chip memory
location; the destination type specifies whether it is a DM or
PM access. The falling edge of the address latch signal latches
this value into the IDMAA register.
Once the address is stored, data can then be either read from, or
written to, the ADSP-21mod870’s on-chip memory. Asserting
the select line (IS) and the appropriate read or write line (IRD
and IWR respectively) signals the ADSP-21mod870 that a par-
ticular transaction is required. In either case, there is a one-
processor-cycle delay for synchronization. The memory access
consumes one additional processor cycle.
Once an access has occurred, the latched address is automati-
cally incremented, and another access can occur.
Through the IDMAA register, the processor can also specify the
starting address and data format for DMA operation. Asserting
the IDMA port select (IS) and address latch enable (IAL)
directs the ADSP-21mod870 to write the address onto the
IAD[14:0] bus into the IDMA Control Register. If IAD[15]
is set to 0, IDMA latches the address. If IAD[15] is set to 1,
IDMA latches OVLAY memory. This register, shown below, is
memory mapped at address DM (0x3FE0). Note that the latched
address (IDMAA) cannot be read back by the host.
REV. 0
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