STM690/704/795/802/804/805/806
6/32
Pin Descriptions
MR (Manual Reset).
A logic low on /MR asserts
the reset output. Reset remains asserted as long
as MR is low and for t
rec
after MR returns high.
This active-low input has an internal pull-up. It can
be driven from a TTL or CMOS logic line, or short-
ed to ground with a switch. Leave open if unused.
WDI (Watchdog Input).
If WDI remains high or
low for 1.6sec, the internal watchdog timer runs
out and reset is triggered. The internal watchdog
timer clears while reset is asserted or when WDI
sees a rising or falling edge.
The watchdog function cannot be disabled by al-
lowing the WDI pin to float.
RST (Active-low Reset).
Pulses low for t
rec
when triggered, and stays low whenever V
CC
is
below the reset threshold or when MR is a logic
low. It remains low for t
rec
after either V
CC
rises
above the reset threshold, the watchdog triggers a
reset, or MR goes from low to high.
RST (Active-high Reset - Open Drain).
Pulses
high for t
rec
when triggered, and stays high when-
ever V
CC
is above the reset threshold or when MR
is a logic high. It remains high for t
rec
after either
V
CC
falls below the reset threshold, the watchdog
triggers a reset, or MR goes from high to low.
PFI (Power-fail Input).
When PFI is less than
V
PFI
or when V
CC
falls below V
SW
(2.4V), PFO
goes low; otherwise, PFO remains high. Connect
to ground if unused.
PFO (Power-fail Output).
When PFI is less than
V
PFI
, or V
CC
falls below V
SW
, PFO goes low; oth-
erwise, PFO remains high. Leave open if unused.
V
OUT
(Supply Output Voltage).
When V
CC
is
above the switchover voltage (V
SO
), V
OUT
is con-
nected to V
CC
through a P-channel MOSFET
switch. When V
CC
falls below V
SO
, V
BAT
connects
to V
OUT
. Connect to V
CC
if no battery is used.
Vccsw (V
CC
Switch Output).
When
switches to battery, Vccsw is high. When V
OUT
switches back to V
CC
, Vccsw is low. It can be used
to drive gate of external PMOS transistor for I
OUT
requirements exceeding 75mA.
V
OUT
E (Chip Enable Input).
The input to the chip-en-
able gating circuit. Connect to ground if unused.
E
CON
(Conditional Chip Enable).
E
CON
low only when E is low and reset is not asserted. If
E
CON
is low when reset is asserted, E
CON
will re-
main low for 15μs or until E goes high, whichever
occurs first. In the disabled mode, E
CON
is pulled
up to V
OUT
.
goes
V
BAT
(Back-up Battery Input).
When V
CC
falls
below V
SO
, V
OUT
switches from V
CC
to V
BAT
.
When V
CC
rises above V
SO
+ hysteresis, V
OUT
re-
connects to V
CC
. V
BAT
may exceed V
CC
. Connect
to V
CC
if no battery is used.
Table 3. Pin Description
Pin
Name
Function
STM795
STM690
STM802
STM704
STM806
STM804
STM805
–
–
6
–
MR
Push-button Reset Input
–
6
–
6
WDI
Watchdog Input
7
7
7
–
RST
Active-Low Reset Output
–
–
–
7
RST
Active-High Reset Output
–
4
4
4
PFI
Power-fail Input
–
5
5
5
PFO
Power-fail Output
1
1
1
1
V
OUT
Supply Output for External LPSRAM
2
2
2
2
V
CC
Supply Voltage
3
–
–
–
Vccsw
V
CC
Switch Output
4
3
3
3
V
SS
Ground
5
–
–
–
E
Chip Enable Input
6
–
–
–
E
CON
Conditioned Chip Enable Output
8
8
8
8
V
BAT
Backup-Battery Input