M93C86 datasheet(19/37 Pages) STMICROELECTRONICS

19 / 37 page

M93C86, M93C76, M93C66, M93C56, M93C46

Clock pulse counter

Doc ID 4997 Rev 10

19/37

Clock pulse counter

In a noisy environment, the number of pulses received on Serial Clock (C) may be greater

than the number delivered by the master (the microcontroller). This can lead to a

misalignment of the instruction of one or more bits (as shown in Figure 7.) and may lead to

the writing of erroneous data at an erroneous address.

To combat this problem, the M93Cx6 has an on-chip counter that counts the clock pulses

from the start bit until the falling edge of the Chip Select Input (S). If the number of clock

pulses received is not the number expected, the WRITE, ERASE, ERAL or WRAL

instruction is aborted, and the contents of the memory are not modified.

The number of clock cycles expected for each instruction, and for each member of the

M93Cx6 family, are summarized in Table 5. to Table 7.. For example, a Write Data to

Memory (WRITE) instruction on the M93C56 (or M93C66) expects 20 clock cycles (for the

x8 organization) from the start bit to the falling edge of Chip Select Input (S). That is:

1 Start bit

+ 2 Op-code bits

+ 9 Address bits

+ 8 Data bits

Figure 7.

Write sequence with one clock glitch

AI01395

An-1

WRITE

START

"1"

"0"

Glitch

An-2

ADDRESS AND DATA

ARE SHIFTED BY ONE BIT

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