PIC17C752 datasheet(59/306 Pages) MICROCHIP

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 1998-2013 Microchip Technology Inc.

DS30289C-page 59

PIC17C7XX

8.0

TABLE READS AND TABLE

WRITES

The PIC17C7XX has four instructions that allow the

processor 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

memory.

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 Microprocessor or Extended

Microcontroller mode.

Figure 8-1 through Figure 8-4 show the operation of

these four instructions. The steps show the sequence

of operation.

FIGURE 8-1:

TLWT

INSTRUCTION

OPERATION

FIGURE 8-2:

TABLWT

INSTRUCTION

OPERATION

TABLE POINTER

TABLE LATCH (16-bit)

Program Memory

Data

Memory

TBLPTRH

TBLPTRL

TABLATH

TABLATL

TLWT 1,f

TLWT 0,f

Step 1: 8-bit value from register 'f', loaded into the high or low

byte in TABLAT (16-bit).

TABLE POINTER

TABLE LATCH (16-bit)

Program Memory

Data

Memory

TBLPTRH

TBLPTRL

TABLATH

TABLATL

TABLWT 1,i,f

TABLWT 0,i,f

Prog-Mem

(TBLPTR)

Step 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.

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