Microchip Technology MA330020 Datenbogen
dsPIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/X04
DS70000318G-page 80
2008-2014 Microchip Technology Inc.
4.6.2
DATA ACCESS FROM PROGRAM
MEMORY USING TABLE
INSTRUCTIONS
MEMORY USING TABLE
INSTRUCTIONS
The TBLRDL and TBLWTL instructions offer a direct
method of reading or writing the lower word of any
address within the program space without going
through data space. The TBLRDH and TBLWTH
instructions are the only method to read or write the
upper 8 bits of a program space word as data.
method of reading or writing the lower word of any
address within the program space without going
through data space. The TBLRDH and TBLWTH
instructions are the only method to read or write the
upper 8 bits of a program space word as data.
The PC is incremented by two for each successive
24-bit program word. This allows program memory
addresses to directly map to data space addresses.
Program memory can thus be regarded as two 16-bit
wide word address spaces, residing side by side, each
with the same address range. TBLRDL and TBLWTL
access the space that contains the least significant
data word. TBLRDH and TBLWTH access the space that
contains the upper data byte.
24-bit program word. This allows program memory
addresses to directly map to data space addresses.
Program memory can thus be regarded as two 16-bit
wide word address spaces, residing side by side, each
with the same address range. TBLRDL and TBLWTL
access the space that contains the least significant
data word. TBLRDH and TBLWTH access the space that
contains the upper data byte.
Two table instructions are provided to move byte or
word-sized (16-bit) data to and from program space.
Both function as either byte or word operations.
word-sized (16-bit) data to and from program space.
Both function as either byte or word operations.
• TBLRDL (Table Read Low):
- In Word mode, this instruction maps the
lower word of the program space location
(P<15:0>) to a data address (D<15:0>).
(P<15:0>) to a data address (D<15:0>).
- In Byte mode, either the upper or lower byte
of the lower program word is mapped to the
lower byte of a data address. The upper byte
is selected when byte select is ‘1’; the lower
byte is selected when it is ‘0’.
lower byte of a data address. The upper byte
is selected when byte select is ‘1’; the lower
byte is selected when it is ‘0’.
• TBLRDH (Table Read High):
- In Word mode, this instruction maps the entire
upper word of a program address (P<23:16>)
to a data address. Note that D<15:8>, the
‘phantom byte’, will always be ‘0’.
to a data address. Note that D<15:8>, the
‘phantom byte’, will always be ‘0’.
- In Byte mode, this instruction maps the upper
or lower byte of the program word to D<7:0> of
the data address, in the TBLRDL instruction.
The data is always ‘0’ when the upper
‘phantom’ byte is selected (Byte Select = 1).
the data address, in the TBLRDL instruction.
The data is always ‘0’ when the upper
‘phantom’ byte is selected (Byte Select = 1).
Similarly, two table instructions, TBLWTH and TBLWTL,
are used to write individual bytes or words to a program
space address. The details of their operation are
explained in
are used to write individual bytes or words to a program
space address. The details of their operation are
explained in
.
For all table operations, the area of program memory
space to be accessed is determined by the Table Page
register (TBLPAG). TBLPAG covers the entire program
memory space of the device, including user and con-
figuration spaces. When TBLPAG<7> = 0, the table
page is located in the user memory space. When
TBLPAG<7> = 1, the page is located in configuration
space.
space to be accessed is determined by the Table Page
register (TBLPAG). TBLPAG covers the entire program
memory space of the device, including user and con-
figuration spaces. When TBLPAG<7> = 0, the table
page is located in the user memory space. When
TBLPAG<7> = 1, the page is located in configuration
space.
FIGURE 4-10:
ACCESSING PROGRAM MEMORY WITH TABLE INSTRUCTIONS
0
8
16
23
00000000
00000000
00000000
00000000
‘Phantom’ Byte
TBLRDH.B
(Wn<0> = 0)
TBLRDL.W
TBLRDL.B
(Wn<0> = 1)
TBLRDL.B
(Wn<0> = 0)
23
15
0
TBLPAG
02
0x000000
0x800000
0x020000
0x030000
Program Space
The address for the table operation is determined by the data EA
within the page defined by the TBLPAG register.
Only read operations are shown; write operations are also valid in
the user memory area.
within the page defined by the TBLPAG register.
Only read operations are shown; write operations are also valid in
the user memory area.