PIC18CXX2
TBLRD
Table Read
TBLRD
Table Read (cont’d)
TBLRD *+ ;
Syntax:
[ label ] TBLRD ( *; *+; *-; +*)
None
Example1:
Operands:
Operation:
Before Instruction
TABLAT
TBLPTR
=
=
=
0x55
0x00A356
0x34
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;
MEMORY(0x00A356)
After Instruction
TABLAT
TBLPTR
=
=
0x34
0x00A357
TBLRD +* ;
Example2:
Before Instruction
TABLAT
TBLPTR
=
=
=
=
0xAA
0x01A357
0x12
MEMORY(0x01A357)
MEMORY(0x01A358)
0x34
After Instruction
TABLAT
TBLPTR
=
=
0x34
0x01A358
Status Affected: None
0000
0000
0000
10nn
nn=0 *
=1 *+
=2 *-
=3 +*
Encoding:
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:
1
2
Q Cycle Activity:
Q1
Q2
Q3
Q4
Decode
No
No
No
operation
operation
operation
No
No
No
No
operation
operation
(Read
operation
operation
(Write
Program
Memory)
TABLAT)
7/99 Microchip Technology Inc.
Preliminary
DS39026B-page 231
MICROCHIP [ MICROCHIP ]
