DSPIC30F2011 Datasheet, PDF (33/207 Pages) Microchip Technology – High-Performance Digital Signal Controllers

dsPIC30F2011/2012/3012/3013
FIGURE 3-5:
PROGRAM DATA TABLE ACCESS (MS BYTE)
TBLRDH.W
PC Address
23
16
8
0
0x000000
00000000
0x000002
00000000
0x000004
00000000
0x000006
00000000
Program Memory
‘Phantom’ Byte
(read as ‘0’)
TBLRDH.B (Wn<0> = 0)
TBLRDH.B (Wn<0> = 1)
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 3-6), 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 Programmer’s Reference Manual (DS70030) for
details on instruction encoding.
Note that by incrementing the PC by 2 for each
program 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 3-6.
Note: PSV access is temporarily disabled during
table reads/writes.
For instructions that use PSV which are executed
outside a REPEAT loop:
• The following instructions will require one
instruction 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.
© 2005 Microchip Technology Inc.
Preliminary
DS70139C-page 31