Texas Instruments TMS320C28x, Reference Manual

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Introduction to the CPU
1-2
1.1 Introduction to the CPU
The CPU is a low-cost 32-bit fixed-point digital signal processor (DSP). This
device draws from the best features of digital signal processing; reduced
instruction set computing (RISC); and microcontroller architectures, firmware,
and tool sets. The DSP features include a modified Harvard architecture and
circular addressing. The RISC features are single-cycle instruction execution,
register-to-register operations, and modified Harvard architecture (usable in
Von Neumann mode). The microcontroller features include ease of use
through an intuitive instruction set, byte packing and unpacking, and bit manip-
ulation.
The modified Harvard architecture of the CPU enables instruction and data
fetches to be performed in parallel. The CPU can read instructions and data
while it writes data simultaneously to maintain the single-cycle instruction op-
eration across the pipeline. The CPU does this over six separate address/data
buses.
1.1.1 Compatibility With Other TMS320 CPUs
The C28x DSP features compatibility modes that minimize the migration effort
from the C27x and C2xLP CPUs. The operating mode of the device is
determined by a combination of the OBJMODE and AMODE bits in status
register 1 (ST1) as shown in Table 1
− 1. The OBJMODE bit allows you to select
between code compiled for a C28x (OBJMODE == 1) and code compiled for
a C27x (OBJMODE == 0). The AMODE bit allows you to select between
C28x/C27x instruction addressing modes (AMODE == 0) and C2xLP
compatible instruction addressing modes (AMODE == 1).
Table 1 − 1. Compatibility Modes
OBJMODE AMODE
C28x Mode 1 0
C2xLP Source-compatible Mode 1 1
C27x Object-compatible Mode
†
0 0
†
The C28x is in C27x-compatible mode at reset.
-
C28x Mode: In C28x mode, you can take advantage of all the C28x native
features, addressing modes, and instructions. To operate in C28x mode
from reset, your code must first set the OBJMODE bit by using the
”C28OBJ” (or ”SETC OBJMODE”) instruction. This book assumes you are
operating in C28x mode unless stated otherwise.
-
C2xLP Source-Compatible Mode: C2xLP source-compatible mode al-
lows you to run C2xLP source code which has been reassembled using