70592C Datasheet, PDF (61/314 Pages) Microchip Technology – High-Performance, 16-bit Microcontrollers

PIC24HJXXXGPX06A/X08A/X10A
4.4.2
DATA ACCESS FROM PROGRAM
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 instruc-
tions 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,
word wide address spaces, residing side by side, each
with the same address range. TBLRDL and TBLWTL
access the space which contains the least significant
data word and TBLRDH and TBLWTH access the space
which 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.
1. TBLRDL (Table Read Low): In Word mode, it
maps the lower word of the program space
location (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’.
2. TBLRDH (Table Read High): In Word mode, it
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’.
In Byte mode, it maps the upper or lower byte of
the program word to D<7:0> of the data
address, as above. Note that the data will
always be ‘0’ when the upper ‘phantom’ byte is
selected (Byte Select = 1).
In a similar fashion, 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 Section 5.0 “Flash
Program Memory”.
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 config-
uration 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 4-7:
ACCESSING PROGRAM MEMORY WITH TABLE INSTRUCTIONS
TBLPAG
02
23
15
Program Space
0 _0x000000
0x020000
0x030000
23
16
00000000
00000000
00000000
00000000
8
0
‘Phantom’ Byte
0x800000
TBLRDH.B (Wn<0> = 0)
TBLRDL.B (Wn<0> = 1)
TBLRDL.B (Wn<0> = 0)
TBLRDL.W
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.
© 2011 Microchip Technology Inc.
DS70592C-page 61