M95040, M95020, M95010
Signal description
2.6
Write Protect (W)
This input signal is used to control whether the memory is write protected. When Write
Protect (W) is held Low, writes to the memory are disabled, but other operations remain
enabled. Write Protect (W) must either be driven High or Low, but must not be left floating.
2.7
V
SS
ground
V
SS
is the reference for the V
CC
supply voltage.
2.8
Supply voltage (V
CC
)
V
CC
is the supply voltage.
2.8.1
Operating supply voltage V
CC
Prior to selecting the memory and issuing instructions to it, a valid and stable V
CC
voltage
within the specified [V
CC
(min), V
CC
(max)] range must be applied (see
and
In order to secure a stable DC supply voltage, it is recommended to decouple the
V
CC
line with a suitable capacitor (usually of the order of 10nF to 100nF) close to the
V
CC
/V
SS
package pins.
This voltage must remain stable and valid until the end of the transmission of the instruction
and, for a Write instruction, until the completion of the internal write cycle (t
W
).
2.8.2
Power-up conditions
When the power supply is turned on, V
CC
rises from V
SS
to V
CC
. During this time, the Chip
Select (S) signal is not allowed to float and must follow the V
CC
voltage. The S line should
therefore be connected to V
CC
via a suitable pull-up resistor.
In addition, the Chip Select (S) input offers a built-in safety feature, as it is both edge
sensitive and level sensitive. Practically this means that after power-up, the device cannot
become selected until a falling edge has first been detected on Chip Select (S). So the Chip
Select (S) signal must first have been High, and then gone Low before the first operation can
be started.
2.8.3
Internal device reset
In order to prevent inadvertent Write operations during Power-up, a Power On Reset (POR)
circuit is included. At Power-up (continuous rise of V
CC
), the device will not respond to any
instruction until V
CC
has reached the Power On Reset threshold voltage (this threshold is
lower than the minimum V
CC
operating voltage defined in
9/42
STMICROELECTRONICS [ STMICROELECTRONICS ]
