Datasheet

2010 Microchip Technology Inc. DS39616D-page 321
PIC18F2331/2431/4331/4431
TBLRD Table Read
Syntax: [ label ] 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 0000 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: 1
Cycles: 2
Q Cycle Activity:
Q1 Q2 Q3 Q4
Decode No
operation
No
operation
No
operation
No
operation
No operation
(Read Program
Memory)
No
operation
No operation
(Write
TABLAT)
TBLRD Table Read (cont’d)
Example 1: TBLRD *+ ;
Before Instruction
TABLAT = 0x55
TBLPTR = 0x00A356
MEMORY(0x00A356) = 0x34
After Instruction
TABLAT = 0x34
TBLPTR = 0x00A357
Example 2: TBLRD +* ;
Before Instruction
TABLAT = 0xAA
TBLPTR = 0x01A357
MEMORY(0x01A357) = 0x12
MEMORY(0x01A358) = 0x34
After Instruction
TABLAT = 0x34
TBLPTR = 0x01A358