dsPIC30F6010
DS70119B-page 22
Advance Information
2004 Microchip Technology Inc.
FIGURE 3-4:
PROGRAM DATA TABLE ACCESS (MS BYTE)
3.1.2
DATA ACCESS FROM PROGRAM
MEMORY USING PROGRAM
SPACE VISIBILITY
The upper 32 Kbytes of data space may optionally be
mapped into any 16K word program space page. This
provides transparent access of stored constant data
from X data space, without the need to use special
instructions (i.e.,
TBLRDL/H, TBLWTL/H
instructions).
Program space access through the data space occurs
if the MS bit of the data space EA is set and program
space visibility is enabled, by setting the PSV bit in the
Core Control register (CORCON). The functions of
CORCON are discussed in Section 2.4, DSP Engine.
Data accesses to this area add an additional cycle to
the instruction being executed, since two program
memory fetches are required.
Note that the upper half of addressable data space is
always part of the X data space. Therefore, when a
DSP operation uses program space mapping to access
this memory region, Y data space should typically con-
tain state (variable) data for DSP operations, whereas
X data space should typically contain coefficient
(constant) data.
Although each data space address, 0x8000 and higher,
maps directly into a corresponding program memory
address (see Figure 3-5), only the lower 16-bits of the
24-bit program word are used to contain the data. The
upper 8 bits should be programmed to force an illegal
instruction to maintain machine robustness. Refer
to the
dsPIC30F Programmer’s Reference Manual
(DS70030) for details on instruction encoding.
Note that by incrementing the PC by 2 for each pro-
gram memory word, the LS 15 bits of data space
addresses directly map to the LS 15 bits in the corre-
sponding program space addresses. The remaining
bits are provided by the Program Space Visibility Page
register, PSVPAG<7:0>, as shown in Figure 3-5.
For instructions that use PSV which are executed
outside a REPEAT loop:
• The following instructions will require one instruc-
tion cycle in addition to the specified execution
time:
-
MAC
class of instructions with data operand
pre-fetch
-
MOV
instructions
-
MOV.D
instructions
• All other instructions will require two instruction
cycles in addition to the specified execution time
of the instruction.
For instructions that use PSV which are executed
inside a REPEAT loop:
• The following instances will require two instruction
cycles in addition to the specified execution time
of the instruction:
- Execution in the first iteration
- Execution in the last iteration
- Execution prior to exiting the loop due to an
interrupt
- Execution upon re-entering the loop after an
interrupt is serviced
• Any other iteration of the REPEAT loop will allow
the instruction, accessing data using PSV, to
execute in a single cycle.
0
8
16
PC Address
0x000000
0x000002
0x000004
0x000006
23
00000000
00000000
00000000
00000000
Program Memory
‘Phantom’ Byte
(Read as ‘
0
’)
TBLRDH.W
TBLRDH.B (Wn<0> = 1)
TBLRDH.B (Wn<0> = 0)
Note:
PSV access is temporarily disabled during
Table Reads/Writes.
Summary of Contents for dsPIC30F6010
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