PIC18F242 datasheet(58/332 Pages) MICROCHIP

58 / 332 page

PIC18FXX2

DS39564C-page 56

FIGURE 5-2:

TABLE WRITE OPERATION

5.2

Control Registers

Several control registers are used in conjunction with

the TBLRD and TBLWT instructions. These include the:

• EECON1 register

• EECON2 register

• TABLAT register

• TBLPTR registers

5.2.1

EECON1 AND EECON2 REGISTERS

EECON1 is the control register for memory accesses.

EECON2 is not a physical register. Reading EECON2

will read all '0's. The EECON2 register is used

exclusively in the memory write and erase sequences.

Control bit EEPGD determines if the access will be a

program or data EEPROM memory access. When

clear, any subsequent operations will operate on the

data EEPROM memory. When set, any subsequent

operations will operate on the program memory.

Control bit CFGS determines if the access will be to the

configuration registers or to program memory/data

EEPROM memory. When set, subsequent operations

will operate on configuration registers, regardless of

EEPGD

(see

“Special

Features

the

CPU”,

Section 19.0). When clear, memory selection access is

determined by EEPGD.

The FREE bit, when set, will allow a program memory

erase operation. When the FREE bit is set, the erase

operation is initiated on the next WR command. When

FREE is clear, only writes are enabled.

The WREN bit, when set, will allow a write operation.

On power-up, the WREN bit is clear. The WRERR bit is

set when a write operation is interrupted by a MCLR

Reset or a WDT Time-out Reset during normal opera-

tion. In these situations, the user can check the

WRERR bit and rewrite the location. It is necessary to

reload the data and address registers (EEDATA and

EEADR), due to RESET values of zero.

Control bit WR initiates write operations. This bit cannot

be cleared, only set, in software. It is cleared in hard-

ware at the completion of the write operation. The

inability to clear the WR bit in software prevents the

accidental

premature

termination

write

operation.

Table Pointer(1)

Table Latch (8-bit)

TBLPTRH

TBLPTRL

TABLAT

Program Memory

(TBLPTR)

TBLPTRU

Instruction: TBLWT*

Note

1: Table Pointer actually points to one of eight holding registers, the address of which is determined by

TBLPTRL<2:0>. The process for physically writing data to the Program Memory Array is discussed in

Section 5.5.

Holding Registers

Program Memory

Note:

Interrupt flag bit EEIF, in the PIR2 register,

is set when the write is complete. It must

be cleared in software.

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