M93C46, M93C56, M93C66, M93C76, M93C86

Clock pulse counter

Doc ID 4997 Rev 12

17/34

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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 avoid 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: Instruction set for the M93C46 to Table 7:

Instruction set for the M93C76 and M93C86. 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

S

An-1

C

D

WRITE

START

D0

"1"

"0"

An

Glitch

An-2

ADDRESS AND DATA

ARE SHIFTED BY ONE BIT