VRD312 datasheet(74/416 Pages) MICROCHIP

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6.6.1

PROGRAMMING ALGORITHM FOR

FLASH PROGRAM MEMORY

The user can program one row of Flash program memory

at a time. To do this, it is necessary to erase the 8-row

erase block containing the desired row. The general

process is:

Read

eight

rows

program

memory

(1024 instructions) and store in data RAM.

Update the program data in RAM with the

desired new data.

Erase the block (see Example 6-1):

Set the NVMOP<3:0> bits (NVMCON<3:0>)

to ‘0011’ to configure for block erase. Set the

WREN (NVMCON<14>) bit.

Write the starting address of the block to

be erased into the NVMADRU/NVMADR

registers.

Write 55h to NVMKEY.

Write AAh to NVMKEY.

Set the WR bit (NVMCON<15>). The erase

cycle begins and the CPU stalls for the dura-

tion of the erase cycle. When the erase is

done, the WR bit is cleared automatically.

Update the TBLPAG register to point to the pro-

gramming latches on the device. Update the

NVMADRU/NVMADR registers to point to the

destination in the program memory.

Write the first 128 instructions from data RAM into

the program memory buffers (see Table 6-1).

Write the program block to Flash memory:

a) Set the NVMOPx bits to ‘0010’ to configure

for row programming. Set the WREN bit.

b) Write 55h to NVMKEY.

Write AAh to NVMKEY.

d) Set the WR bit. The programming cycle

begins and the CPU stalls for the duration

of the write cycle. When the write to Flash

memory is done, the WR bit is cleared

automatically.

Repeat Steps 4 through 6, using the next

available 128 instructions from the block in data

RAM, by incrementing the value in NVMADRU/

NVMADR until all 1024 instructions are written

back to Flash memory.

For protection against accidental operations, the write

initiate sequence for NVMKEY must be used to allow

any erase or program operation to proceed. After the

programming command has been executed, the user

must wait for the programming time until programming

is complete. The two instructions following the start of

the programming sequence should be NOPs, as shown

in Example 6-2.

TABLE 6-1:

EXAMPLE PAGE ERASE

Step 1: Set the NVMCON register to erase a page.

MOV

#0x4003, W0

MOV

W0, NVMCON

Step 2: Load the address of the page to be erased into the NVMADR register pair.

MOV

#PAGE_ADDR_LO, W0

MOV

W0, NVMADR

MOV

#PAGE_ADDR_HI, W0

MOV

W0, NVMADRU

Step 3: Set the WR bit.

MOV

#0x55, W0

MOV

W0, NVMKEY

MOV

#0xAA, W0

MOV

W0, NVMKEY

BSET

NVMCON, #WR

NOP

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