
PIC18F1230/1330
DS39758D-page 74
2009 Microchip Technology Inc.
7.2.2
TABLAT – TABLE LATCH REGISTER
The Table Latch (TABLAT) is an 8-bit register mapped
into the SFR space. The Table Latch register is used to
hold 8-bit data during data transfers between program
memory and data RAM.
7.2.3
TBLPTR – TABLE POINTER
REGISTER
The Table Pointer (TBLPTR) register addresses a byte
within the program memory. The TBLPTR is comprised
of three SFR registers: Table Pointer Upper Byte,
Table Pointer High Byte and Table Pointer Low Byte
(TBLPTRU:TBLPTRH:TBLPTRL).
These
three
registers join to form a 22-bit wide pointer. The low-
order 21 bits allow the device to address up to
2 Mbytes of program memory space. The 22nd bit
allows access to the device ID, the user ID and the
Configuration bits.
The Table Pointer register, TBLPTR, is used by the
TBLRD
and TBLWT instructions. These instructions can
update the TBLPTR in one of four ways based on the
table operation. These operations are shown in
Table 7-1. These operations on the TBLPTR only affect
the low-order 21 bits.
7.2.4
TABLE POINTER BOUNDARIES
TBLPTR is used in reads, writes and erases of the
Flash program memory.
When a TBLRD is executed, all 22 bits of the TBLPTR
determine which byte is read from program memory
into TABLAT.
When the timed write to program memory begins (via
the WR bit), the 19 MSbs of the TBLPTR
(TBLPTR<21:3>) determine which program memory
block of 8 bytes is written to. The Table Pointer regis-
ter’s three LSBs (TBLPTR<2:0>) are ignored. For more
When an erase of program memory is executed, the
16 MSbs of the Table Pointer register (TBLPTR<21:6>)
point to the 64-byte block that will be erased. The Least
Significant bits (TBLPTR<5:0>) are ignored.
TBLPTR based on Flash program memory operations.
TABLE 7-1:
TABLE POINTER OPERATIONS WITH TBLRD AND TBLWT INSTRUCTIONS
FIGURE 7-3:
TABLE POINTER BOUNDARIES BASED ON OPERATION
Example
Operation on Table Pointer
TBLRD*
TBLWT*
TBLPTR is not modified
TBLRD*+
TBLWT*+
TBLPTR is incremented after the read/write
TBLRD*-
TBLWT*-
TBLPTR is decremented after the read/write
TBLRD+*
TBLWT+*
TBLPTR is incremented before the read/write
21
16
15
87
0
TABLE ERASE
TABLE WRITE
TABLE READ – TBLPTR<21:0>
TBLPTRL
TBLPTRH
TBLPTRU
TBLPTR<21:3>
TBLPTR<21:6>