adm9240 Analog Devices, Inc., adm9240 Datasheet - Page 14

• Manufacturer Part Number: adm9240
• Description: Low Cost Microprocessor System Hardware Monitor
• Manufacturer: Analog Devices, Inc.

ADM9240
The chassis intrusion circuit should be designed so that it can be
reset by pulling its output low. A suitable chassis intrusion cir-
cuit using a phototransistor is shown in Figure 8. Light falling
on the phototransistor when the PC cover is removed will cause
it to turn on and pull up the input of N1, thus setting the latch
N3/N4. After the cover is replaced, a low reset on the CI output
will pull down the input of N4, resetting the latch.
The Chassis Intrusion input can also be used for other types of
alarm input. Figure 8b shows a temperature alarm circuit using
an AD22105 temperature switch sensor. This produces a low-
going output when the preset temperature is exceeded, so the
output is inverted by Q1 to make it compatible with the CI
input. Q1 can be almost any small-signal NPN transistor, or a
TTL or CMOS inverter gate may be used if one is available. See
the AD22105 data sheet for information on selecting R
FROM VALUE
REGISTERS
AND LIMIT
BATTERY
BACKUP
Figure 8a. Chassis Intrusion Detector and Latch
CMOS
HIGH LIMIT
LOW LIMIT
VALUE
MRD901
1N914
470k
COMPARATORS
LOW LIMIT
HIGH AND
74HC132
OF LIMIT
1 = OUT
CI (CHASSIS INTRUSION)
Figure 9. Interrupt Register Structure
100k
DEMULTIPLEXER
1N914
MASKING DATA
DATA
SET
CI
10k
FROM BUS
+5V
.
+V
–14–
+V
+2.5V
+3.3V
FAN2
TEMP
FAN1
+12V
CCP2
+5V
CCP1
Note: The chassis intrusion input does not have a protective
clamp diode to V
sion latch and reset it when the ADM9240 was powered down.
THE ADM9240 INTERRUPT STRUCTURE
The Interrupt Structure of the ADM9240 is shown in Figure 9.
As each measurement value is obtained and stored in the
appropriate value register, the value and the limits from the
corresponding limit registers are fed to the high and low limit
comparators. The result of each comparison (1 = out of limit,
0 = in limit) is routed to the corresponding bit input of the
Interrupt Status Registers via a data demultiplexer and used to
set that bit high or low as appropriate.
The Interrupt Mask Registers have bits corresponding to each of
the Interrupt Status Register Bits. Setting an Interrupt Mask Bit
high forces the corresponding Status Bit output low, while set-
ting an Interrupt Mask Bit low allows the corresponding Status
Bit to be asserted. After masking, the status bits are all ORed
together to produce the INT output, which will pull low if any
unmasked status bit goes high, i.e., when any measured value
goes out of limit.
The INT output is enabled when Bit 1 of the Configuration
Register (INT_Enable) is high, and Bit 3 (INT_Clear) is low.
Figure 8b. Using the CI Input with a Temperature Sensor
INTERRUPT
REGISTERS
INTERRUPT
REGISTERS
STATUS
MASK
R
SET
STATUS
MASK
MASK GATING
BIT
CC
BIT
AD22105
, as this could pull down the chassis intru-
SENSOR
TEMP.
10
Q1
R1
10k
INT_ENABLE
V
CONFIGURATION
C
REGISTER
CI
INT_CLEAR
REV. 0
INT