PIC18F2455_07 Datasheet, PDF (348/430 Pages) Microchip Technology – 28/40/44-Pin, High Performance, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
TBLWT
Table Write
Syntax:
TBLWT ( *; *+; *-; +*)
Operands:
None
Operation:
if TBLWT*
(TABLAT) → Holding Register;
TBLPTR – No Change;
if TBLWT*+
(TABLAT) → Holding Register;
(TBLPTR) + 1 → TBLPTR;
if TBLWT*-
(TABLAT) → Holding Register;
(TBLPTR) – 1 → TBLPTR;
if TBLWT+*
(TBLPTR) + 1 → TBLPTR;
(TABLAT) → Holding Register
Status Affected: None
Encoding:
Description:
0000 0000 0000
11nn
nn=0 *
=1 *+
=2 *-
=3 +*
This instruction uses the 3 LSBs of TBLPTR
to determine which of the
8 holding registers the TABLAT is written to.
The holding registers are used to
program the contents of Program
Memory (P.M.). (Refer to Section 6.0
“Flash Program Memory” for additional
details on programming Flash memory.)
The TBLPTR (a 21-bit pointer) points to
each byte in the program memory. TBLPTR
has a 2-Mbyte address range. The LSb of
the TBLPTR selects which byte of the
program memory location to access.
TBLPTR[0] = 0: Least Significant
Byte of Program
Memory Word
TBLPTR[0] = 1: Most Significant
Byte of Program
Memory Word
The TBLWT 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
No
No
operation operation operation
No
No
No
operation operation operation
(Read
TABLAT)
No
operation
(Write to
Holding
Register)
TBLWT
Table Write (Continued)
Example 1:
TBLWT *+;
Before Instruction
TABLAT
=
TBLPTR
=
HOLDING REGISTER
(00A356h)
=
55h
00A356h
FFh
After Instructions (table write completion)
TABLAT
=
TBLPTR
=
HOLDING REGISTER
(00A356h)
=
55h
00A357h
55h
Example 2:
TBLWT +*;
Before Instruction
TABLAT
=
TBLPTR
=
HOLDING REGISTER
(01389Ah)
=
HOLDING REGISTER
(01389Bh)
=
34h
01389Ah
FFh
FFh
After Instruction (table write completion)
TABLAT
=
TBLPTR
=
HOLDING REGISTER
(01389Ah)
=
HOLDING REGISTER
(01389Bh)
=
34h
01389Bh
FFh
34h
DS39632D-page 346
Preliminary
© 2007 Microchip Technology Inc.