
CPU Primary Register File
3-4
Figure 3–1.Extended-Precision Register Floating-Point Format
mantissa
fraction (f)
s
39
32 31
30
0
e
For integer operations, bits 31–0 of the extended-precision registers contain
the integer (signed or unsigned). Any instruction that assumes that the oper-
ands are either signed or unsigned integers uses only bits 31–0. Bits 39–32
remain unchanged. This is true for all shift operations. The storage of 32-bit
integers in the extended-precision registers is shown in Figure 3–2.
Figure 3–2.Extended-Precision Register Integer Format
39
signed or unsigned integer
unchanged
32 31
0
3.1.2
Auxiliary Registers (AR0–AR7)
The eight 32-bit auxiliary registers (AR0–AR7) can be accessed by the CPU
and modified by the two auxiliary register arithmetic units (ARAUs). The prima-
ry function of the auxiliary registers is the generation of 32-bit addresses. How-
ever, they can also operate as loop counters in indirect addressing or as 32-bit
general-purpose registers that can be modified by the multiplier and ALU. See
Chapter 6, Addressing Modes for detailed information and examples of the
use of auxiliary registers in addressing.
3.1.3
Data-Page Pointer (DP)
The data-page pointer (DP) is a 32-bit register whose 16 LSBs are used by the
direct addressing mode as a pointer to the page of data being addressed. Data
pages are 64K words long with a total of 64K (65,536) pages.
Bits 31–16 are
reserved; they are always read as zeros and should not be modified by writing
to the register The DP can be loaded by using the LDP pseudoinstruction or
the LDI instruction. Figure 6–1, on page 6-5, describes this register’s func-
tions.
3.1.4
Index Registers (IR0, IR1)
The 32-bit index registers (IR0 and IR1) are used by the auxiliary register arith-
metic unit (ARAU) for indexing the address. IR0 is also used for bit-reversed
addressing. See Chapter 6, Addressing Modes for detailed information and
examples of the use of index registers in addressing. Section 6.4, Indirect Ad-
dressing on page 6-6, discusses and provides examples of using IRnin indi-
rect addressing. Section 6.9, Bit-Reversed Addressing on page 6-32, de-
scribes using IRnwith bit-reversed addressing.