PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 70

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18FXX8
6.2.2
The Table Latch (TABLAT) is an 8-bit register mapped
into the SFR space. The Table Latch is used to hold
8-bit data during data transfers between program
memory and data RAM.
6.2.3
The Table Pointer (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 pro-
gram 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 oper-
ation. These operations are shown in Table 6-1. These
operations on the TBLPTR only affect the low order 21
bits.
TABLE 6-1:
FIGURE 6-3:
DS41159B-page 68
TBLRD*+
TBLWT*+
TBLRD*-
TBLWT*-
TBLRD+*
TBLWT+*
Example
TBLRD*
TBLWT*
21
TABLAT - TABLE LATCH REGISTER
TBLPTR - TABLE POINTER
REGISTER
TABLE POINTER OPERATIONS WITH TBLRD AND TBLWT INSTRUCTIONS
TBLPTRU
TABLE POINTER BOUNDARIES BASED ON OPERATION
16
ERASE - TBLPTR<21:6>
15
TBLPTR is incremented before the read/write
TBLPTR is decremented after the read/write
TBLPTR is incremented after the read/write
WRITE - TBLPTR<21:3>
TBLPTRH
Preliminary
Operation on Table Pointer
READ - TBLPTR<21:0>
TBLPTR is not modified
6.2.4
TBLPTR is used in reads, writes, and erases of the
FLASH program memory.
When a TBLRD is executed, all 22 bits of the Table
Pointer determine which byte is read from program
memory into TABLAT.
When a TBLWT is executed, the three LSbs of the Table
Pointer (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 Table Pointer, TBLPTR
(TBLPTR<21:3>), will determine which program mem-
ory block of 8 bytes is written to. For more detail, see
Section 6.5,Writing to FLASH Program Memory.
When an erase of program memory is executed, the 16
MSbs of the Table Pointer (TBLPTR<21:6>) point to the
64-byte block that will be erased. The Least Significant
bits (TBLPTR<5:0>) are ignored.
Figure 6-3 describes the relevant boundaries of
TBLPTR
operations.
8
7
based
TABLE POINTER BOUNDARIES
on
TBLPTRL
 2002 Microchip Technology Inc.
FLASH
program
0
memory