Texas Instruments TMS320C28x User Manual

Memory Interface
1-11Architectural Overview
Table 1−3. Special Bus Operations
Instruction
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Special Bus Operation
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PREAD
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This instruction reads a data value rather than an instruction from pro-
gram space. It then transfers that value to data space or a register.
For the read from program space, the CPU places the source address
on the program address bus (PAB), sets the appropriate program-
space select signals, and reads the data value from the program-read
data bus (PRDB).
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PWRITE
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This instruction writes a data value to program space. The value is
read from from data space or a register.
For the write to program space, the CPU places the destination ad-
dress on the program address bus (PAB), sets the appropriate pro-
gram-space select signals, and writes the data value to the data-/pro-
gram-write data bus (DWDB).
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MAC
DMAC
QMACL
IMACL
XMAC
XMACD
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As part of their operation, these instructions multiply two data values,
one of which is read from program space.
For the read from program space, the CPU places the program-space
source address on the program address bus (PAB), sets the appropri-
ate program-space select signals, and reads the program data value
from the program read data bus (PRDB).
1.4.3 Alignment of 32-Bit Accesses to Even Addresses
The C28x CPU expects memory wrappers or peripheral-interface logic to align
any 32-bit read or write to an even address. If the address-generation logic
generates an odd address, the CPU must begin reading or writing at the pre-
vious even address. This alignment does not affect the address values gener-
ated by the address-generation logic.
Most instruction fetches from program space are performed as 32-bit read op-
erations and are aligned accordingly. However, alignment of instruction
fetches are effectively invisible to a programmer. When instructions are stored
to program space, they do not have to be aligned to even addresses. Instruc-
tion boundaries are decoded within the CPU.
You need to be concerned with alignment when using instructions that perform
32-bit reads from or writes to data space.

Texas Instruments TMS320C28x Specifications

General

Brand	Texas Instruments
Model	TMS320C28x
Category	Processor
Language	English