Datasheet

 1996 Microchip Technology Inc. DS30412C-page 43
PIC17C4X
7.0 TABLE READS AND TABLE
WRITES
The PIC17C4X has four instructions that allow the pro-
cessor to move data from the data memory space to
the program memory space, and vice versa. Since the
program memory space is 16-bits wide and the data
memory space is 8-bits wide, two operations are
required to move 16-bit values to/from the data mem-
ory.
The TLWT t,f and TABLWT t,i,f instructions are
used to write data from the data memory space to the
program memory space. The TLRD t,f and TABLRD
t,i,f instructions are used to write data from the pro-
gram memory space to the data memory space.
The program memory can be internal or external. For
the program memory access to be external, the device
needs to be operating in extended microcontroller or
microprocessor mode.
Figure 7-1 through Figure 7-4 show the operation of
these four instructions.
FIGURE 7-1: TLWT INSTRUCTION
OPERATION
TABLE POINTER
TABLE LATCH (16-bit)
PROGRAM MEMORY
DATA
MEMORY
TBLPTRH
TBLPTRL
TABLATH TABLATL
f
TLWT 1,f TLWT 0,f
1
Note 1: 8-bit value, from register 'f', loaded into the
high or low byte in TABLAT (16-bit).
FIGURE 7-2: TABLWT INSTRUCTION
OPERATION
TABLE POINTER
TABLE LATCH (16-bit)
PROGRAM MEMORY
DATA
MEMORY
TBLPTRH
TBLPTRL
TABLATH TABLATL
f
TABLWT 1,i,f TABLWT 0,i,f
1
Prog-Mem
(TBLPTR)
2
Note 1: 8-bit value, from register 'f', loaded into
the high or low byte in TABLAT (16-bit).
2: 16-bit TABLAT value written to address
Program Memory (TBLPTR).
3: If “i” = 1, then TBLPTR = TBLPTR + 1,
If “i” = 0, then TBLPTR is unchanged.
3
3
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