PIC18CXX2
Table Read operations retrieve data from program
memory and place it into the Data memory space.
Figure 5-1 shows the operation of a Table Read with
program and data memory.
5.0
TABLE READS/TABLE WRITES
Enhanced devices have two memory spaces: the pro-
gram memory space and the data memory space. The
program memory space is 16 bits wide, while the data
memory space is 8 bits wide. Table Reads and Table
Writes have been provided to move data between
these two memory spaces through an 8 bit register
(TABLAT).
Table Write operations store data from the data mem-
ory space into program memory. Figure 5-2 shows the
operation of a Table Write with program and data mem-
ory.
Table operations work with byte entities. A table block
containing data is not required to be word aligned, so a
table block can start and end at any byte address. If a
table write is being used to write an executable program
to program memory, program instructions will need to
be word aligned.
The operations that allow the processor to move data
between the data and program memory spaces are:
• Table Read (TBLRD)
• Table Write (TBLWT)
FIGURE 5-1: TABLE READ OPERATION
(1)
TABLE LATCH (8-bit)
TABLAT
TABLE POINTER
TBLPTRU TBLPTRH TBLPTRL
PROGRAM MEMORY
Program Memory
(TBLPTR)
Instruction: TBLRD*
Note 1: Table Pointer points to a byte in
program memory
FIGURE 5-2: TABLE WRITE OPERATION
(1)
TABLE LATCH (8-bit)
TABLAT
TABLE POINTER
TBLPTRU TBLPTRH TBLPTRL
PROGRAM MEMORY
Program Memory
(TBLPTR)
Instruction: TBLWT*
Note 1: Table Pointer points to a byte in
program memory
7/99 Microchip Technology Inc.
Preliminary
DS39026B-page 53
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