PIC18LF452 Microchip Technology, PIC18LF452 Datasheet - Page 57

• Manufacturer Part Number: PIC18LF452
• Description: (PIC18LFxx2) Enhanced FLASH Microcontrollers
• Manufacturer: Microchip Technology

5.0
The FLASH Program Memory is readable, writable,
and erasable during normal operation over the entire
V
A read from program memory is executed on one byte
at a time. A write to program memory is executed on
blocks of 8 bytes at a time. Program memory is erased
in blocks of 64 bytes at a time. A bulk erase operation
may not be issued from user code.
Writing or erasing program memory will cease instruc-
tion fetches until the operation is complete. The pro-
gram memory cannot be accessed during the write or
erase, therefore, code cannot execute. An internal pro-
gramming timer terminates program memory writes
and erases.
A value written to program memory does not need to be
a valid instruction. Executing a program memory
location that forms an invalid instruction results in a
NOP.
FIGURE 5-1:
DD
2002 Microchip Technology Inc.
range.
Note 1: Table Pointer points to a byte in program memory.
TBLPTRU
FLASH PROGRAM MEMORY
Table Pointer
TBLPTRH
TABLE READ OPERATION
(1)
TBLPTRL
Program Memory
(TBLPTR)
Instruction: TBLRD *
Program Memory
5.1
In order to read and write program memory, there are
two operations that allow the processor to move bytes
between the program memory space and the data
RAM:
• Table Read (TBLRD)
• Table Write (TBLWT)
The program memory space is 16-bits wide, while the
data RAM space is 8-bits wide. Table Reads and Table
Writes move data between these two memory spaces
through an 8-bit register (TABLAT).
Table Read operations retrieve data from program
memory and places it into the data RAM space.
Figure 5-1 shows the operation of a Table Read with
program memory and data RAM.
Table Write operations store data from the data mem-
ory space into holding registers in program memory.
The procedure to write the contents of the holding reg-
isters into program memory is detailed in Section 5.5,
'”Writing to FLASH Program Memory”. Figure 5-2
shows the operation of a Table Write with program
memory and data RAM.
Table operations work with byte entities. A table block
containing data, rather than program instructions, is not
required to be word aligned. Therefore, a table block
can start and end at any byte address. If a Table Write
is being used to write executable code into program
memory, program instructions will need to be word
aligned.
Table Reads and Table Writes
PIC18FXX2
Table Latch (8-bit)
TABLAT
DS39564B-page 55