Datasheet

PIC18F1220/1320
DS39605F-page 230 © 2007 Microchip Technology Inc.
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-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
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)
Example 1: 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