TMS28F400BZT, TMS28F400BZB

524288 BY 8-BIT/262144 BY 16-BIT

BOOT-BLOCK FLASH MEMORIES

SMJS400E – JUNE 1994 – REVISED JANUARY 1998

10

POST OFFICE BOX 1443

normal programming

There are two CSM commands for programming: program setup and alternate program setup

(see Table 1 ). After the desired command code is entered, the WSM takes over and correctly sequences the

device to complete the program operation. During this time, the CSM responds only to status reads until the

program operation has been completed, after which all commands to the CSM become valid again. Once a

program command has been issued, the WSM cannot normally be interrupted until the program algorithm has

operation. If 1s are programmed, the memory cell contents do not change and no error occurs.

A program-setup command can be aborted by writing FFh ( in byte-wide mode) or FFFFh ( in word-wide mode)

during the second cycle. After writing all 1s during the second cycle, the CSM responds only to status reads.

When the WSM status bit (SB7) is set to a logic-high level, signifying the nonprogram operation is terminated,

all commands to the CSM become valid again.

erase operations

There are two erase operations that can be performed by the TMS28F400BZx devices: block erase and erase

suspend / erase resume. An erase operation must be used to initialize all bits in an array block to 1s. After

block-erase confirm is issued, the CSM responds only to status reads or erase-suspend commands until the

WSM completes its task.

Block erasure inside the memory array sets all bits within the addressed block to logic 1s. Erasure is

accomplished only by blocks; data at single address locations within the array cannot be individually erased.

changing the data content of the boot block. Block erasure is initiated by a command sequence to the CSM:

block-erase setup (20h) followed by block-erase confirm (D0h) (see Figure 5). A two-command erase

sequence protects against accidental erasure of memory contents.

Erase setup and confirm commands are latched on the rising edge of E or W, whichever occurs first. Block

addresses are latched during the block-erase-confirm command on the rising edge of E or W (see Figure 10

and Figure 11 ). When the block-erase-confirm command is complete, the WSM automatically executes a

sequence of events to complete the block erasure. During this sequence, the block is programmed with

logic 0s, data is verified, all bits in the block are erased, and finally, verification is performed to ensure that all

bits are correctly erased. Monitoring of the erase operation is possible through the status register (see the

subsection, “read status register”).

During the execution of an erase operation, the erase-suspend command (B0h ) can be entered to direct the

WSM to suspend the erase operation. Once the WSM has reached the suspend state, it allows the CSM to

respond only to the read-array, read-status-register, and erase-resume commands. During the

erase-suspend operation, array data should be read from a block other than the one being erased. To

resume the erase operation, an erase-resume command (D0h ) must be issued to cause the CSM to clear

the suspend state previously set (see Figure 5 and Figure 6).

automatic power-saving mode

Substantial power savings are realized during periods when the array is not being read. During this time, the

operation is initiated. In this mode, the I/O pins retain the data from the last memory-address read until a new

address is read. This mode is entered automatically if no address or control pins toggle within a 200-ns time-out

period. At least one transition on E must occur after power up to activate this mode.