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5.7.2 Program Models
5.7.3 Register Conventions
5.7.4 Status Registers
TMS320C28x Rules and Guidelines
Only large memory model is supported for the program memory. So no special program memory
requirements are needed for this processor. Just to reemphasize the point, all the program code must be
completely relocatable and must not necessarily require placement in on-chip memory.
This section describes the rules and guidelines that apply to the use of the TMS320C28x on-chip
registers. Note that any register that is not described here must not be accessed by an algorithm; e.g.,
IMR, IFR, and peripheral control and status register. The table below describes all the registers that may
be accessed by an algorithm.
Register
Use
Type
AL
Expressions, argument passing, and returns 16-bit results from functions
Scratch (local)
AH
Expressions and argument passing
Scratch (local)
XAR0
Pointers and expressions
Scratch (local)
XAR1
Pointers and expressions
Preserve (local)
XAR2
Pointers, expressions, and frame pointers
Preserve (local)
XAR3
Pointers and expressions
Preserve (local)
XAR4
Pointers, expressions, argument passing, and returns 16- and 22-bit
Scratch (local)
pointer values from functions
XAR5
Pointers, expressions, and arguments
Scratch (local)
XAR6
Pointers and expressions
Scratch (local)
XAR7
Pointers, expressions, indirect calls, and branches
Scratch (local)
SP
Stack pointer
Preserve (local)
T
Multiply and shift expressions
Scratch (local)
TL
Multiply and shift expressions
Scratch (local)
PL
Multiply expressions and Temp variables
Scratch (local)
PH
Multiply expressions and Temp variables
Scratch (local)
DP
Data page pointer
Scratch (local)
The TMS320C28x device contains two-status registers: ST0 and ST1. Each status register is further
divided into several distinct fields that may be accessed separately using special instructions like SETC,
CLRC, SPM, etc.
ST0 Field Name
Use
Type
OVC/OVCU
Overflow counter
Scratch (local)
PM
Produce shift mode
Init (local)
V
Overflow flag
Scratch (local)
N
Negative flag
Scratch (local)
Z
Zero flag
Scratch (local)
C
Carry flag
Scratch (local)
TC
Test/Control flag
Scratch (local)
OVM
Overflow mode
Scratch (local)
SXM
Sign extension mode
Scratch (local)
SPRU352G – June 2005 – Revised February 2007
DSP-Specific Guidelines
59
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