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ADSP-2185BST-133 Datasheet(PDF) 9 Page - Analog Devices |
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ADSP-2185BST-133 Datasheet(HTML) 9 Page - Analog Devices |
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9 / 32 page  ADSP-2185 –9– REV. 0 selected memory select signal. All enable bits, except the BMS bit, default to 1 at reset, Byte Memory The byte memory space is a bidirectional, 8-bit-wide, external memory space used to store programs and data. Byte memory is accessed using the BDMA feature. The byte memory space consists of 256 pages, each of which is 16K × 8. The byte memory space on the ADSP-2185 supports read and write operations as well as four different data formats. The byte memory uses data bits 15:8 for data. The byte memory uses data bits 23:16 and address bits 13:0 to create a 22-bit address. This allows up to a 4 meg × 8 (32 megabit) ROM or RAM to be used without glue logic. All byte memory accesses are timed by the BMWAIT register. Byte Memory DMA (BDMA, Full Memory Mode) The Byte memory DMA controller allows loading and storing of program instructions and data using the byte memory space. The BDMA circuit is able to access the byte memory space while the processor is operating normally and steals only one DSP cycle per 8-, 16- or 24-bit word transferred. The BDMA circuit supports four different data formats, which are selected by the BTYPE register field. The appropriate num- ber of 8-bit accesses are done from the byte memory space to build the word size selected. Table V shows the data formats supported by the BDMA circuit. Table V. Internal BTYPE Memory Space Word Size Alignment 00 Program Memory 24 Full Word 01 Data Memory 16 Full Word 10 Data Memory 8 MSBs 11 Data Memory 8 LSBs 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 starting 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. 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 gener- ated. The BMPAGE and BEAD registers must not be accessed by the DSP during BDMA operations. The source or destination of a BDMA transfer will always be on-chip program or data memory, regardless of the values of Mode B, PMOVLAY or DMOVLAY. 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 DSP cycle. DSP 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 to start execution at address 0 when the BDMA accesses have completed. 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-2185. The port is used to access the on-chip program memory and data memory of the DSP with only one DSP cycle per word overhead. The IDMA port cannot, however, be used to write to the DSP’s memory- mapped control registers. 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- 2185 is operating at full speed. The DSP memory address is latched and then automatically 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 in- creases 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-2185’s on-chip memory. Asserting the select line ( IS) and the appropriate read or write line (IRD and IWR respectively) signals the ADSP-2185 that a particular 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 DSP can also specify the starting address and data format for DMA operation. Bootstrap Loading (Booting) The ADSP-2185 has two mechanisms to allow automatic load- ing of the internal program memory after reset. The method for booting is controlled by the Mode A, B and C configuration bits as shown in Table VI. These four states can be compressed into two-state bits by allowing an IDMA boot with Mode C = 1. However, three bits are used to ensure future compatibility with parts containing internal program memory ROM. BDMA Booting When the MODE pins specify BDMA booting, the ADSP-2185 initiates a BDMA boot sequence when RESET is released. |
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