Datasheet

© 2008-2012 Microchip Technology Inc. DS70318F-page 29
dsPIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/X04
3.0 CPU
The CPU module has a 16-bit (data) modified Harvard
architecture with an enhanced instruction set, including
significant support for DSP. The CPU has a 24-bit
instruction word with a variable length opcode field.
The Program Counter (PC) is 23 bits wide and
addresses up to 4M x 24 bits of user program memory
space. The actual amount of program memory
implemented varies from device to device. A single-
cycle instruction prefetch mechanism is used to help
maintain throughput and provides predictable
execution. All instructions execute in a single cycle,
with the exception of instructions that change the
program flow, the double-word move (MOV.D)
instruction and the table instructions. Overhead-free
program loop constructs are supported using the DO
and REPEAT instructions, both of which are
interruptible at any point.
dsPIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/
X04 devices have sixteen, 16-bit working registers in
the programmer’s model. Each of the working registers
can serve as a data, address or address offset register.
The sixteenth working register (W15) operates as a
software Stack Pointer (SP) for interrupts and calls.
There are two classes of instruction in the
ds PIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/
X04
devices: MCU and DSP. These two instruction
classes are seamlessly integrated into a single CPU.
The instruction set includes many addressing modes
and is designed for optimum C compiler efficiency.
For most instructions, the dsPIC33FJ06GS101/X02
and dsPIC33FJ16GSX02/X04 is capable of execut-
ing a data (or program data) memory read, a work-
ing register (data) read, a data memory write and a
program (instruction) memory read per instruction
cycle. As a result, three parameter instructions can
be supported, allowing A + B = C operations to be
executed in a single cycle.
A block diagram of the CPU is shown in Figure 3-1,
and the programmer’s model is shown in Figure 3-2.
3.1 Data Addressing Overview
The data space can be addressed as 32K words or
64 Kbytes and is split into two blocks, referred to as X
and Y data memory. Each memory block has its own
independent Address Generation Unit (AGU). The
MCU class of instructions operates solely through
the X memory AGU, which accesses the entire
memory map as one linear data space. Certain DSP
instructions operate through the X and Y AGUs to
support dual operand reads, which splits the data
address space into two parts. The X and Y data space
boundary is device-specific.
Overhead-free circular buffers (Modulo Addressing
mode) are supported in both X and Y address spaces.
The Modulo Addressing removes the software
boundary checking overhead for DSP algorithms.
Furthermore, the X AGU circular addressing can be
used with any of the MCU class of instructions. The X
AGU also supports Bit-Reversed Addressing to greatly
simplify input or output data reordering for radix-2 FFT
algorithms.
The upper 32 Kbytes of the data space memory map
can optionally be mapped into program space at any
16K program word boundary defined by the 8-bit
Program Space Visibility Page (PSVPAG) register. The
program-to-data space mapping feature allows any
instruction access program space as if it were data
space.
3.2 DSP Engine Overview
The DSP engine features a high-speed, 17-bit by 17-bit
multiplier, a 40-bit ALU, two 40-bit saturating
accumulators and a 40-bit bidirectional barrel shifter.
The barrel shifter is capable of shifting a 40-bit value up
to 16 bits, right or left, in a single cycle. The DSP
instructions operate seamlessly with all other
instructions and have been designed for optimal real-
time performance. The MAC instruction and other asso-
ciated instructions can concurrently fetch two data
operands from memory while multiplying two W
registers and accumulating and optionally saturating
the result in the same cycle. This instruction
functionality requires that the RAM data space be split
for these instructions and linear for all others. Data
space partitioning is achieved in a transparent and
flexible manner through dedicating certain working
registers to each address space.
Note 1: This data sheet summarizes the features
of the dsPIC33FJ06GS101/X02 and
dsPIC33FJ16GSX02/X04 families of
devices. It is not intended to be a
comprehensive reference source. To
complement the information in this data
sheet, refer to Section 2. “CPU”
(DS70204) in the “dsPIC33F/PIC24H
Family Reference Manual”, which is
available from the Microchip web site
(www.microchip.com).
2: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.