Datasheet

© 2007 Microchip Technology Inc. DS39599G-page 297
PIC18F2220/2320/4220/4320
TBLWT Table Write
Syntax: [ label ] 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:
0000 0000 0000 11nn
nn=0 *
=1 *+
=2 *-
=3 +*
Description: 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 MBtye 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
TBLWT Table Write (Continued)
Words: 1
Cycles: 2
Q Cycle Activity:
Q1 Q2 Q3 Q4
Decode No
operation
No
operation
No
operation
No
operation
No
operation
(Read
TABLAT)
No
operation
No
operation
(Write to
Holding
Register )
Example1: TBLWT *+;
Before Instruction
TABLAT = 0x55
TBLPTR = 0x00A356
HOLDING REGISTER
(0x00A356) = 0xFF
After Instructions (table write completion)
TABLAT = 0x55
TBLPTR = 0x00A357
HOLDING REGISTER
(0x00A356) = 0x55
Example 2: TBLWT +*;
Before Instruction
TABLAT = 0x34
TBLPTR = 0x01389A
HOLDING REGISTER
(0x01389A) = 0xFF
HOLDING REGISTER
(0x01389B) = 0xFF
After Instruction (table write completion)
TABLAT = 0x34
TBLPTR = 0x01389B
HOLDING REGISTER
(0x01389A) = 0xFF
HOLDING REGISTER
(0x01389B) = 0x34