AFS090 datasheet(62/334 Pages) MICROSEMI

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Device Architecture

2- 46

R e visio n 2

Data operations are performed in widths of 1 to 4 bytes. A write to a location in a page that is not already

in the Page Buffer will cause the page to be read from the FB Array and stored in the Page Buffer. The

block that was addressed during the write will be put into the Block Buffer, and the data written by WD will

overwrite the data in the Block Buffer. After the data is written to the Block Buffer, the Block Buffer is then

written to the Page Buffer to keep both buffers in sync. Subsequent writes to the same block will

overwrite the Block Buffer and the Page Buffer. A write to another block in the page will cause the

addressed block to be loaded from the Page Buffer, and the write will be performed as described

previously.

The data width can be selected dynamically via the DATAWIDTH input bus. The truth table for the data

width settings is detailed in Table 2-21. The minimum resolvable address is one 8-bit byte. For data

widths greater than 8 bits, the corresponding address bits are ignored—when DATAWIDTH = 0 (2 bytes),

ADDR[0] is ignored, and when DATAWIDTH = '10' or '11' (4 bytes), ADDR[1:0] are ignored. Data pins are

LSB-oriented and unused WD data pins must be grounded.

Flash Memory Block Protection

Page Loss Protection

When the PAGELOSSPROTECT pin is set to logic 1, it prevents writes to any page other than the

current page in the Page Buffer until the page is either discarded or programmed.

A write to another page while the current page is Page Loss Protected will return a STATUS of '11'.

Overwrite Protection

Any page that is Overwrite Protected will result in the STATUS being set to '01' when an attempt is made

to either write, program, or erase it. To set the Overwrite Protection state for a page, set the

OVERWRITEPROTECT pin when a Program operation is undertaken. To clear the Overwrite Protect

state for a given page, an Unprotect Page operation must be performed on the page, and then the page

must be programmed with the OVERWRITEPROTECT pin cleared to save the new page.

LOCKREQUEST

The LOCKREQUEST signal is used to give the user interface control over simultaneous access of the FB

from both the User and JTAG interfaces. When LOCKREQUEST is asserted, the JTAG interface will hold

off any access attempts until LOCKREQUEST is deasserted.

Flash Memory Block Operations

FB Operation Priority

The FB provides for priority of operations when multiple actions are requested simultaneously.

Table 2-22 shows the priority order (priority 0 is the highest).

Table 2-21 • Data Width Settings

DATAWIDTH[1:0]

Data Width

1 byte [7:0]

2 byte [15:0]

10, 11

4 bytes [31:0]

Table 2-22 • FB Operation Priority

Operation

Priority

System Initialization

FB Reset

Read

Write

Erase Page

Program

Unprotect Page

Discard Page

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