PIC18F2420/2520/4420/4520
TBLRD
Table Read
TBLRD
Table Read (Continued)
Syntax:
TBLRD ( *; *+; *-; +*)
None
Example1:
TBLRD *+ ;
Operands:
Operation:
Before Instruction
TABLAT
TBLPTR
MEMORY (00A356h)
=
=
=
55h
00A356h
34h
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
After Instruction
TABLAT
TBLPTR
=
=
34h
00A357h
Example2:
TBLRD +* ;
Before Instruction
TABLAT
TBLPTR
MEMORY (01A357h)
MEMORY (01A358h)
After Instruction
=
=
=
=
AAh
01A357h
12h
34h
TABLAT
TBLPTR
=
=
34h
01A358h
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:MostSignificantByteof
Program Memory
Word
The TBLRDinstruction can modify the value
of TBLPTR as follows:
•
•
•
•
no change
post-increment
post-decrement
pre-increment
Words:
Cycles:
1
2
Q Cycle Activity:
Q1
Q2
No
Q3
No
Q4
Decode
No
operation
operation
operation
No
No operation
No
No operation
operation (Read Program operation (Write TABLAT)
Memory)
© 2008 Microchip Technology Inc.
DS39631E-page 305
MICROCHIP [ MICROCHIP ]
