dspic33fj128mc204 Microchip Technology Inc., dspic33fj128mc204 Datasheet - Page 44

• Manufacturer Part Number: dspic33fj128mc204
• Description: High-performance, 16-bit Digital Signal Controllers
• Manufacturer: Microchip Technology Inc.

4.2.5
The core has two data spaces, X and Y. These data
spaces can be considered either separate (for some
DSP instructions), or as one unified linear address
range (for MCU instructions). The data spaces are
accessed using two Address Generation Units (AGUs)
and separate data paths. This feature allows certain
instructions to concurrently fetch two words from RAM,
thereby enabling efficient execution of DSP algorithms
such as Finite Impulse Response (FIR) filtering and
Fast Fourier Transform (FFT).
The X data space is used by all instructions and
supports all addressing modes. X data space has
separate read and write data buses. The X read data
bus is the read data path for all instructions that view
data space as combined X and Y address space. It is
also the X data prefetch path for the dual operand DSP
instructions (MAC class).
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
provide two concurrent data read paths.
Both the X and Y data spaces support Modulo
Addressing mode for all instructions, subject to
addressing mode restrictions. Bit-Reversed Addressing
mode is only supported for writes to X data space.
All data memory writes, including in DSP instructions,
view data space as combined X and Y address space.
The boundary between the X and Y data spaces is
device-dependent and is not user-programmable.
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, though the
implemented memory locations vary by device.
DS70291C-page 42
X AND Y DATA SPACES
Preliminary
4.2.6
Every
dsPIC33FJ64MCX02/X04,
dsPIC33FJ128MCX02/X04 device contains up to 2
Kbytes of dual ported DMA RAM located at the end of
Y data space, and is a part of Y data space. Memory
locations in the DMA RAM space are accessible
simultaneously by the CPU and the DMA controller
module. DMA RAM is utilized by the DMA controller to
store data to be transferred to various peripherals
using DMA, as well as data transferred from various
peripherals using DMA. The DMA RAM can be
accessed by the DMA controller without having to
steal cycles from the CPU.
When the CPU and the DMA controller attempt to
concurrently write to the same DMA RAM location, the
hardware ensures that the CPU is given precedence in
accessing the DMA RAM location. Therefore, the DMA
RAM provides a reliable means of transferring DMA
data without ever having to stall the CPU.
Note:
DMA RAM
DMA RAM can be used for general
purpose data storage if the DMA function
is not required in an application.
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