M93C86, M93C76, M93C66, M93C56, M93C46
CLOCK PULSE COUNTER
READY/BUSY STATUS
While the Write or Erase cycle is underway, for a
WRITE, ERASE, WRAL or ERAL instruction, the
Busy signal (Q=0) is returned whenever Chip Se-
lect Input (S) is driven High. (Please note, though,
In a noisy environment, the number of pulses re-
ceived on Serial Clock (C) may be greater than the
number delivered by the master (the microcontrol-
ler). This can lead to a misalignment of the instruc-
tion of one or more bits (as shown in Figure 7.) and
may lead to the writing of erroneous data at an er-
roneous 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 In-
put (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.
that there is an initial delay, of t
, before this
SLSH
status information becomes available). In this
state, the M93Cx6 ignores any data on the bus.
When the Write cycle is completed, and Chip Se-
lect Input (S) is driven High, the Ready signal
(Q=1) indicates that the M93Cx6 is ready to re-
ceive the next instruction. Serial Data Output (Q)
remains set to 1 until the Chip Select Input (S) is
brought Low or until a new start bit is decoded.
The number of clock cycles expected for each in-
struction, and for each member of the M93Cx6
family, are summarized in Table 5. to Table 7.. For
example, a Write Data to Memory (WRITE) in-
struction 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:
COMMON I/O OPERATION
Serial Data Output (Q) and Serial Data Input (D)
can be connected together, through a current lim-
iting resistor, to form a common, single-wire data
bus. Some precautions must be taken when oper-
ating the memory in this way, mostly to prevent a
short circuit current from flowing when the last ad-
dress bit (A0) clashes with the first data bit on Se-
rial Data Output (Q). Please see the application
note AN394 for details.
1 Start bit
+ 2 Op-code bits
+ 9 Address bits
+ 8 Data bits
Figure 7. Write Sequence with One Clock Glitch
S
C
D
An
An-1
Glitch
An-2
START
"0"
"1"
D0
ADDRESS AND DATA
ARE SHIFTED BY ONE BIT
WRITE
AI01395
11/31
STMICROELECTRONICS [ ST ]
