Datasheet

 1999-2013 Microchip Technology Inc. DS39026D-page 225
PIC18CXX2
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