PIC24F32KA304 datasheet(69/320 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

DS39995B-page 69

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6.3

NVM Address Register

As with Flash program memory, the NVM Address

Registers, NVMADRU and NVMADR, form the 24-bit

Effective Address (EA) of the selected row or word for

data EEPROM operations. The NVMADRU register is

used to hold the upper 8 bits of the EA, while the

NVMADR register is used to hold the lower 16 bits of

the EA. These registers are not mapped into the

Special Function Register (SFR) space; instead, they

directly capture the EA<23:0> of the last table write

instruction that has been executed and selects the data

EEPROM row to erase. Figure 6-1 depicts the program

memory EA that is formed for programming and erase

operations.

Like program memory operations, the Least Significant

bit (LSb) of NVMADR is restricted to even addresses.

This is because any given address in the data

EEPROM space consists of only the lower word of the

program memory width; the upper word, including the

uppermost “phantom byte”, are unavailable. This

means that the LSb of a data EEPROM address will

always be ‘0’.

Similarly, the Most Significant bit (MSb) of NVMADRU

is always ‘0’, since all addresses lie in the user program

space.

FIGURE 6-1:

DATA EEPROM ADDRESSING WITH TBLPAG AND NVM ADDRESS REGISTERS

6.4

Data EEPROM Operations

The EEPROM block is accessed using table read and

write operations similar to those used for program

memory. The TBLWTH and TBLRDH instructions are not

required for data EEPROM operations since the

memory is only 16 bits wide (data on the lower address

is valid only). The following programming operations

can be performed on the data EEPROM:

• Erase one, four or eight words

• Bulk erase the entire data EEPROM

• Write one word

• Read one word

The library procedures are used in the code examples

detailed in the following sections. General descriptions

of each process are provided for users who are not

using the C30 compiler libraries.

24-Bit PM Address

TBLPAG

NVMADR

W Register EA

7Fh

xxxxh

NVMADRU

Note 1:

Unexpected results will be obtained if the

user attempts to read the EEPROM while

a programming or erase operation is

underway.

The C30 C compiler includes library

procedures to automatically perform the

table read and table write operations,

manage the Table Pointer and write

buffers, and unlock and initiate memory

write sequences. This eliminates the

need to create assembler macros or time

critical routines in C for each application.

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