OP7100
Hardware 29
Figure 3-3. OP7100 Power-Failure Detection Circuit
Since R34 >> RN2, the difference between V
H
and V
L
, the hysteresis
voltage, would be 5 V × (R30/R34). For a nominal hysteresis voltage of
1.25 V, R
30
= 0.25 × R34.
Memory Protection
When
/RESET
is active, the ADM691 supervisor disables the RAM chip-
select line, preventing accidental writes.
Battery Backup
The backup battery protects data in the RAM and the real-time clock (RTC).
VRAM, the voltage supplied to the RAM and RTC, can also protect other
devices attached to the system against power failures. The ADM691 super-
visor switches VRAM to VBAT or VCC, whichever is greater. (To prevent
“hunting,” the switchover actually occurs when Vcc is 50 mV higher than
VBAT.)
The circuit draws no current from the battery once regular power is applied.
System Reset
The ADM691 chip drives the
/RESET
line. The
/RESET
line is not pulled
up internally.
DCIN
U28 Reg.
VCC
R30
29.4 k
W
R29
4.99 k
W
PFI
to supervisor
VIN
VOUT
C44
47 µF
U12 Supervisor
VBAT
WDI
PFI
VOUT
WDO
PFO
RST
INT1
R34
220 k
W
RST
VCC
RN2
10 k
W
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎠
⎞
⎜
⎝
⎛
+
=
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+
−
⎟
⎠
⎞
⎜
⎝
⎛
+
=
R34
R30
R29
R30
1
V
3
.
1
V
RN2)
V(R34
1.3
V)
1.3
-
V
5
(
R30
R29
R30
1
V
3
.
1
V
H
L
Summary of Contents for OP7100
Page 1: ...OP7100 Serial Graphic Display User s Manual 019 0065 070831 O ...
Page 10: ...OP7100 x About This Manual ...
Page 16: ...OP7100 16 Overview ...
Page 74: ...OP7100 74 Software ...
Page 82: ...OP7100 82 Graphics Programming ...
Page 88: ...OP7100 88 Installation ...
Page 98: ...OP7100 98 Specifications ...
Page 108: ...OP7100 108 Memory I O Map and Interrupt Vectors ...
Page 112: ...112 Serial Interface Board 2 OP7100 ...
Page 113: ...OP7100 Backup Battery 113 APPENDIX E BACKUP BATTERY ...
Page 116: ...OP7100 116 Backup Battery ...
Page 124: ...OP7100 124 Index ...
Page 126: ...XX0000 Schematics ...