NE1617A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 5 — 20 March 2012 10 of 30
NXP Semiconductors
NE1617A
Temperature monitor for microprocessor systems
commands of registers named WIHL, WILL, WEHL, WELL, RIHL, RILL, REHL, RELL,
accordingly. The POR default values are +127 C (0111 1111) for the HIGH limit and
55 C (1100 1001) for the LOW limit.
8.3.6 One-shot command
The one-shot command is not actually a data register as such and a write operation to it
will initiate an ADC conversion. The send byte format of the SMBus, as described later,
with the use of OSHT command (0Fh), is used for this writing operation. In normal
free-running-conversion operation mode of the device, a one-shot command immediately
forces a new conversion cycle to begin. However, if a conversion is in progress when a
one-shot command is received, the command is ignored. In software standby mode the
one-shot command generates a single conversion and comparison cycle and then puts
the device back in its standby mode after the conversion. In hardware standby mode, the
one shot is inhibited.
8.3.7 Status register
The content of the status register reflects condition status resulting from all of these
activities: comparisons between temperature measurements and temperature limits, the
status of ADC conversion, and the hardware condition of the connection of external diode
to the device. Bit assignments and bit functions of this register are listed in Table 8
. This
register can only be read using the command of register named RS. Upon POR, the
status of all flag bits are reset to zero. The status byte is cleared by any successful read of
the status register unless the fault condition persists.
Notice that any one of the fault conditions, except the conversion busy, also introduces an
Alert interrupt to the SMBus that will be described in Section 8.3.8
. Also, whenever a
one-shot command is executed, the status byte should be read after the conversion is
completed, which is about 170 ms after the one-shot command is sent.
[1] These flags stay HIGH until the status register is read or POR is activated.
[2] This flag stays HIGH until POR is activated.
8.3.8 Alert interrupt
The ALERT output is used to signal Alert interruption from the device to the SMBus and is
active LOW. Because this output is an open-drain output, a pull-up resistor (10 k typical)
to V
DD
is required, and slave devices can share a common interrupt line on the same
SMBus. An Alert interrupt is asserted by the device whenever any one of the fault
conditions, as described in Section 8.3.7 “
Status register”, occurs: measured temperature
equals or exceeds corresponding temp limits, the remote diode is physically disconnected
from the device pins. Alert interrupt signal is latched and can only be cleared by reading
Table 8. Status register bit assignment
Bit Symbol POR state Function
7 (MSB) BUSY n/a HIGH when the ADC is busy converting
6IHLF
[1]
0 HIGH when the internal temperature high limit has tripped
5 ILLF
[1]
0 HIGH when the internal temperature low limit has tripped
4EHLF
[1]
0 HIGH when the external temperature high limit has tripped
3ELLF
[1]
0 HIGH when the external temperature low limit has tripped
2OPEN
[2]
0 HIGH when the external diode is opened
1 to 0 - 0 reserved
