M95320 datasheet(18/39 Pages) STMICROELECTRONICS

18 / 39 page

M95640, M95320

18/39

Figure 14. Byte Write (WRITE) Sequence

Note: Depending on the memory size, as shown in Table 6, the most significant address bits are Don’t Care.

Write to Memory Array (WRITE)

As shown in Figure 14, to send this instruction to

the device, Chip Select (S) is first driven Low. The

bits of the instruction byte, address byte, and at

least one data byte are then shifted in, on Serial

Data Input (D).

The instruction is terminated by driving Chip Se-

lect (S) High at a byte boundary of the input data.

In the case of Figure 14, this occurs after the

eighth bit of the data byte has been latched in, in-

dicating that the instruction is being used to write

a single byte. The self-timed Write cycle starts,

and continues for a period tWC (as specified in Ta-

bles 18 to 22), at the end of which the Write in

Progress (WIP) bit is reset to 0.

If, though, Chip Select (S) continues to be driven

Low, as shown in Figure 15, the next byte of input

data is shifted in, so that more than a single byte,

starting from the given address towards the end of

the same page, can be written in a single internal

Write cycle.

Each time a new data byte is shifted in, the least

significant bits of the internal address counter are

incremented. If the number of data bytes sent to

the device exceeds the page boundary, the inter-

nal address counter rolls over to the beginning of

the page, and the previous data there are overwrit-

ten with the incoming data. (The page size of

these devices is 32 bytes).

The instruction is not accepted, and is not execut-

ed, under the following conditions:

– if the Write Enable Latch (WEL) bit has not been

set to 1 (by executing a Write Enable instruction

just before)

– if a Write cycle is already in progress

– if the device has not been deselected, by Chip

Select (S) being driven High, at a byte boundary

(after the eighth bit, b0, of the last data byte that

has been latched in)

– if the addressed page is in the region protected

by the Block Protect (BP1 and BP0) bits.

AI01795D

3456789 10

20 21 22 23 24 25 26 27

14 13

3210

28 29 30

High Impedance

Instruction

16-Bit Address

765432

Data Byte

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