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DSPIC30F6015T-30E/PT 데이터시트(PDF) 30 Page - Microchip Technology |
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DSPIC30F6015T-30E/PT 데이터시트(HTML) 30 Page - Microchip Technology |
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30 / 236 page  dsPIC30F6010A/6015 DS70150C-page 28 © 2007 Microchip Technology Inc. 3.2.2 DATA SPACES The X data space is used by all instructions and sup- ports all addressing modes. There are separate read and write data buses. The X read data bus is the return data path for all instructions that view data space as combined X and Y address space. It is also the X address space data path for the dual operand read instructions (MAC class). The X write data bus is the only write path to data space for all instructions. The X data space also supports Modulo Addressing for all instructions, subject to addressing mode restric- tions. Bit-Reversed Addressing is only supported for writes to X data space. The Y data space is used in concert with the X data space by the MAC class of instructions (CLR, ED, EDAC, MAC, MOVSAC, MPY, MPY.N and MSC) to pro- vide two concurrent data read paths. No writes occur across the Y bus. This class of instructions dedicates two W register pointers, W10 and W11, to always address Y data space, independent of X data space, whereas W8 and W9 always address X data space. Note that during accumulator write-back, the data address space is considered a combination of X and Y data spaces, so the write occurs across the X bus. Consequently, the write can be to any address in the entire data space. The Y data space can only be used for the data prefetch operation associated with the MAC class of instructions. It also supports Modulo Addressing for automated circular buffers. Of course, all other instruc- tions can access the Y data address space through the X data path, as part of the composite linear space. The boundary between the X and Y data spaces is defined as shown in Figure 3-6 and is not user pro- grammable. Should an EA point to data outside its own assigned address space, or to a location outside phys- ical memory, an all-zero word/byte will be returned. For example, although Y address space is visible by all non-MAC instructions using any addressing mode, an attempt by a MAC instruction to fetch data from that space, using W8 or W9 (X space pointers), will return 0x0000. All Effective Addresses are 16 bits wide and point to bytes within the data space. Therefore, the data space address range is 64 Kbytes or 32K words. 3.2.3 DATA SPACE WIDTH The core data width is 16 bits. All internal registers are organized as 16-bit wide words. Data space memory is organized in byte addressable, 16-bit wide blocks. 3.2.4 DATA ALIGNMENT To help maintain backward compatibility with PIC® devices and improve data space memory usage effi- ciency, the dsPIC30F instruction set supports both word and byte operations. Data is aligned in data mem- ory and registers as words, but all data space EAs resolve to bytes. Data byte reads will read the complete word, which contains the byte, using the LSb of any EA to determine which byte to select. The selected byte is placed onto the LSB of the X data path (no byte accesses are possible from the Y data path as the MAC class of instruction can only fetch words). That is, data memory and registers are organized as two parallel byte wide entities with shared (word) address decode, but separate write lines. Data byte writes only write to the corresponding side of the array or register which matches the byte address. As a consequence of this byte accessibility, all Effective Address calculations (including those generated by the DSP operations, which are restricted to word-sized data) are internally scaled to step through word-aligned memory. For example, the core would recognize that Post-Modified Register Indirect Addressing mode, [Ws++], will result in a value of Ws + 1 for byte operations and Ws + 2 for word operations. All word accesses must be aligned to an even address. Misaligned word data fetches are not supported, so care must be taken when mixing byte and word opera- tions, or translating from 8-bit MCU code. Should a misaligned read or write be attempted, an address error trap will be generated. If the error occurred on a read, the instruction underway is completed, whereas if it occurred on a write, the instruction will be executed but the write will not occur. In either case, a trap will then be executed, allowing the system and/or user to examine the machine state prior to execution of the address Fault. FIGURE 3-8: DATA ALIGNMENT TABLE 3-2: EFFECT OF INVALID MEMORY ACCESSES Attempted Operation Data Returned EA = an unimplemented address 0x0000 W8 or W9 used to access Y data space in a MAC instruction 0x0000 W10 or W11 used to access X data space in a MAC instruction 0x0000 15 8 7 0 0001 0003 0005 0000 0002 0004 Byte 1 Byte 0 Byte 3 Byte 2 Byte 5 Byte 4 LSB MSB |
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