PIC18F4520ESLASHMLSTQP datasheet(76/390 Pages) MICROCHIP

76 / 390 page

PIC18F2420/2520/4420/4520

DS39631A-page 74

Preliminary

 2004 Microchip Technology Inc.

FIGURE 6-2:

TABLE WRITE OPERATION

6.2

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

6.2.1

EECON1 AND EECON2 REGISTERS

The EECON1 register (Register 6-1) is the control

not a physical register; it is used exclusively in the

memory

write

and

erase

sequences.

Reading

EECON2 will read all ‘0’s.

The EEPGD control bit 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.

The CFGS control bit determines if the access will be

to the configuration/calibration registers or to program

memory/data

EEPROM

memory.

When

set,

subsequent operations will operate on configuration

registers regardless of EEPGD (see Section 23.0

“Special Features of the CPU”). When clear, memory

selection access is determined by EEPGD.

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

erase operation. When FREE 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 in hardware when the WR bit is set and cleared

when the internal programming timer expires and the

write operation is complete.

The WR control bit initiates write operations. The bit

cannot be cleared, only set, in software; it is cleared in

hardware at the completion of the 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 64 holding registers, the address of which is determined by

TBLPTRL<5:0>. The process for physically writing data to the program memory array is discussed in

Section 6.5 “Writing to Flash Program Memory”.

Holding Registers

Program Memory

Note:

During normal operation, the WRERR is

read as ‘1’. This can indicate that a write

operation was prematurely terminated by

a Reset, or a write operation was

attempted improperly.

Note:

The EEIF interrupt flag bit (PIR2<4>) is set

when the write is complete. It must be

cleared in software.

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