PIC18F6X2X datasheet(68/386 Pages) MICROCHIP

68 / 386 page

PIC18F6X2X/8X2X

DS39612A-page 66

Advance Information

 2003 Microchip Technology Inc.

5.2.2

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.

5.2.3

TBLPTR - TABLE POINTER

The Table Pointer register (TBLPTR) 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 regis-

ters 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, TBLPTR, is used by the TBLRD and

TBLWT

instructions. These instructions can update the

TBLPTR in one of four ways based on the table opera-

tion. These operations are shown in Table 5-1. These

operations on the TBLPTR only affect the low order

21 bits.

5.2.4

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 a TBLWT is executed, the three LSbs of the Table

Pointer register (TBLPTR<2:0>) determine which of the

eight program memory holding registers is written to.

When the timed write to program memory (long write)

begins, the 19 MSbs of the TBLPTR (TBLPTR<21:3>)

will determine which program memory block of 8 bytes

is written to. For more detail, see Section 5.5, “Writing

to FLASH Program Memory”.

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.

Figure 5-3 describes the relevant boundaries of

TBLPTR

based

FLASH

program

memory

operations.

TABLE 5-1:

TABLE POINTER OPERATIONS WITH TBLRD AND TBLWT INSTRUCTIONS

FIGURE 5-3:

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

ERASE - TBLPTR<20:6>

WRITE - TBLPTR<21:3>

READ - TBLPTR<21:0>

TBLPTRL

TBLPTRH

TBLPTRU

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