M35080 datasheet(4/18 Pages) STMICROELECTRONICS

4 / 18 page

M35080

4/18

OPERATIONS

All instructions, addresses and data are shifted se-

rially in and out of the chip (along the bus, as

shown in Figure 4). The most significant bit is pre-

sented first, with the data input (D) sampled on the

first rising edge of the clock (C) after the chip se-

lect (S) goes low (as shown in Figure 5, Figure 9,

and Figure 12).

Every instruction, as summarized in Table 5, starts

with a single-byte code. If an invalid instruction is

sent (one not contained in Table 5), the chip auto-

matically deselects itself.

The instruction code is entered via the data input

(D), and latched on the rising edge of the clock in-

put (C). To enter an instruction code, the device

must have been previously selected (S held low).

Protection of the First 32 Bytes

The first 32-byte page is organized as 16 words

(two bytes each). The initial content of each word

on this page is 0000h. When writing to byte-pair, a

logic comparator verifies that the new two-byte

value is larger than the value currently stored. If

the new value is smaller than the current one, no

operation is performed. It is impossible to write a

value lower than the previous one, irrespective of

the state of W pin and status register, as indicated

in Table 6.

Write Enable (WREN) and Write Disable (WRDI)

The write enable latch, inside the memory device,

must be set prior to each WRITE and WRSR oper-

ation. The WREN instruction (write enable) sets

this latch, and the WRDI instruction (write disable)

resets it.

Figure 4. EEPROM and SPI Bus

AI02148C

M35xxx

CQD

M35xxx

CQD

M35xxx

CQD

CS3

CS2

CS1

SPI Interface with

(CPOL, CPHA) =

('0', '0') or ('1', '1')

Master

(ST6, ST7, ST9,

ST10, Others)

Table 5. Instruction Set

Instruction

Description

Instruction Format

WREN

Set Write Enable Latch

0000 0110

WRDI

Reset Write Enable Latch

0000 0100

RDSR

Read Status Register

0000 0101

WRSR

Write Status Register

0000 0001

READ

Read Data from Memory Array

0000 0011

WRITE

Write Data to Memory Array

0000 0010

WRINC

Write Data to Secure Array

0000 0111

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