PIC18F4520ESLASHMLQTP datasheet(307/390 Pages) MICROCHIP

307 / 390 page

 2004 Microchip Technology Inc.

Preliminary

DS39631A-page 305

PIC18F2420/2520/4420/4520

TBLRD

Table Read

Syntax:

TBLRD ( *; *+; *-; +*)

Operands:

None

Operation:

if TBLRD *,

(Prog Mem (TBLPTR))

→ TABLAT;

TBLPTR – No Change;

if TBLRD *+,

(Prog Mem (TBLPTR))

→ TABLAT;

(TBLPTR) + 1

→ TBLPTR;

if TBLRD *-,

(Prog Mem (TBLPTR))

→ TABLAT;

(TBLPTR) – 1

→ TBLPTR;

if TBLRD +*,

(TBLPTR) + 1

→ TBLPTR;

(Prog Mem (TBLPTR))

→ TABLAT;

Status Affected: None

Encoding:

0000

10nn

nn=0 *

=1 *+

=2 *-

=3 +*

Description:

This instruction is used to read the contents

of Program Memory (P.M.). To address the

program memory, a pointer called Table

Pointer (TBLPTR) is used.

The TBLPTR (a 21-bit pointer) points to

each byte in the program memory. TBLPTR

has a 2-Mbyte address range.

TBLPTR[0] = 0:

Least Significant Byte

of Program Memory

Word

TBLPTR[0] = 1:

Most Significant Byte

of Program Memory

Word

The TBLRD instruction can modify the value

of TBLPTR as follows:

• no change

• post-increment

• post-decrement

• pre-increment

Words:

Cycles:

Q Cycle Activity:

Decode

operation

No operation

(Read Program

Memory)

operation

No operation

(Write TABLAT)

TBLRD

Table Read (Continued)

Example1:

TBLRD

*+ ;

Before Instruction

TABLAT

55h

TBLPTR

00A356h

MEMORY (00A356h)

34h

After Instruction

TABLAT

34h

TBLPTR

00A357h

Example2:

TBLRD

+* ;

Before Instruction

TABLAT

AAh

TBLPTR

01A357h

MEMORY (01A357h)

12h

MEMORY (01A358h)

34h

After Instruction

TABLAT

34h

TBLPTR

01A358h

PIC18F4520E/MLQTP Datasheet(PDF) 307 Page - Microchip Technology

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