m41st87w STMicroelectronics, m41st87w Datasheet - Page 22

• Manufacturer Part Number: m41st87w
• Description: 5.0, 3.3, Or 3.0v, 1280 Bit 160 X8 Secure Serial Rtc And Nvram Supervisor With Tamper Detection
• Manufacturer: STMicroelectronics

M41ST87Y, M41ST87W
Tamper Detection Operation
The Tamper Pins are triggered based on the state
of an external switch. Two switch mode options
are available, “Normally Open” or “Normally
Closed,” based on the setting of the Tamper Con-
nect Mode Bit (TCM
is Normally Open (TCM
be triggered by being connected to V
TPM
set to '1'), through the closing of the external
switch. When the external switch is closed, the
Tamper Bit will be immediately set, allowing the
user to determine if the device has been physically
tampered with. If the selected switch mode is Nor-
mally Closed (TCM
triggered by being pulled to V
pending on the state of the TPM
internal pull-up/pull-down resistor as a result of
opening the external switch.
When a tamper event occurs, the Tamper Bits
(TB1 and/or TB2) will be immediately set if TEB
'1.'
If the Tamper Interrupt Enable Bit (TIE
'1,' the IRQ/OUT pin will also be activated. The
IRQ/OUT output is cleared by a READ of the Flags
Register (as seen in
of the TIE Bit to '0,' or the RST output is enabled.
Note: In order to avoid an inadvertent activation of
the IRQ/OUT pin due to a prior tamper event, the
Flag Register (0Fh) should be read prior to reset-
ting the TEB
The Tamper Bits are “Read only” bits and are reset
only by writing the Tamper Enable Bit (TEB
The Tamper Detect function operates both under
normal power, and in battery back-up. Even if the
trigger event occurs during a power-down condi-
tion, the bit will be set correctly.
22/42
X
Bit is set to '0') or to V
X
Bit.
X
X
). If the selected switch mode
Figure 24., page
= '0'), the Tamper Pin will be
X
= '1'), the Tamper Pin will
CC
SS
(if the TPM
X
or to V
Bit), through an
X
28), a reset
) is set to a
SS
OUT
X
X
) to '0.'
(if the
Bit is
(de-
X
=
Sampling
As the Switch Mode Normally Closed (TCM
requires a greater amount of current to maintain
constant monitoring, the M41ST87Y/W offers a
programmable Tamper Detect Sampling Bit
(TDS
V
the sampling frequency is once per second (1Hz),
for approximately 1ms.
When TEB
by the Tamper Detection Circuit. After a tamper
event has been detected, no additional current will
be drawn.
Note: The oscillator must be running for Tamper
Detection to operate in the sampling mode. If the
oscillator is stopped, the Tamper Detection Circuit
will revert to constant monitoring.
Note: Sampling in the Tamper High Mode
(TPM
connecting the TPX
nal resistor. This will allow constant monitoring
when V
battery back-up (see
Internal Tamper Pull-up/down Current
Depending on the capacitive and resistive loading
of the Tamper Pin Input (TP
quire more or less current from the internal pull-up/
down used when monitoring the Normally Closed
switch mode. The state of the Tamper Current Hi/
Tamper Current Low Bit (TCHI/TCLO
mines the sizing of the internal pull-up/-down.
TCHI/TCLO
sistor, while TCHI/TCLO
up/-down resistor (see
BAT
X
X
(see
) to reduce the current drawn on V
= '1') may be bypassed while on V
CC
is “On” and revert to sampling when in
X
Figure 17., page
X
is disabled, no current will be drawn
= '1' uses a 1M
IN
Figure 14., page
pin to V
Figure 18., page
X
= '0' uses a 10M
XIN
19). When enabled,
CC
), the user may re-
pull-up/-down re-
through an exter-
16).
19).
X
) deter-
X
CC
CC
= '0')
pull-
by
or