DATA ACCESS FROM PROGRAM
MEMORY AND DATA EEPROM
MEMORY USING TABLE
The TBLRDL and TBLWTL instructions offer a direct
method of reading or writing the lower word of any
address within the program memory without going
through data space. It also offers a direct method of
reading or writing a word of any address within data
EEPROM memory. 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 TBLRDH and TBLWTH instructions are
not used while accessing data EEPROM
The PC is incremented by 2 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.
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’.
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).
© 2009 Microchip Technology Inc.
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
For all table operations, the area of program memory
space to be accessed is determined by the Table
Memory Page Address register (TBLPAG). TBLPAG
covers the entire program memory space of the
device, including user and configuration 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.
Only table read operations will execute in
the configuration memory space, and only
then, in implemented areas such as the
Device ID. Table write operations are not