TMP401
SBOS371A AUGUST 2006 REVISED OCTOBER 2007
www.ti.com
11
STATUS REGISTER
The TMP401 has a status register to report the state of the
temperature comparators. Table 4 shows the Status
Register bits. The Status Register is read-only and is read
by reading from pointer address 02h.
The BUSY bit reads as 1 if the ADC is making a
conversion. It reads as 0 if the ADC is not converting.
The OPEN bit reads as 1 if the remote transistor was
detected as open since the last read of the Status Register.
The OPEN status is only detected when the ADC is
attempting to convert a remote temperature.
The RTHRM bit reads as 1 if the remote temperature has
exceeded the remote THERM limit and remains greater
than the remote THERM limit less the value in the shared
hysteresis register; see Figure 17.
The LTHRM bit reads as 1 if the local temperature has
exceeded the local THERM limit and remains greater than
the local THERM limit less the value in the shared
hysteresis register; see Figure 17.
The LHIGH and RHIGH bit values depend on the state of
the AL/TH bit in the Configuration Register. If the AL/TH bit
is 0, the LHIGH bit reads as 1 if the local high limit was
exceeded since the last clearing of the Status Register.
The RHIGH bit reads as 1 if the remote high limit was
exceeded since the last clearing of the Status Register. If
the AL/TH bit is 1, the remote high limit and the local high
limit are used to implement a THERM2
function. LHIGH
reads as 1 if the local temperature has exceeded the local
high limit and remains greater than the local high limit less
the value in the Hysteresis Register.
The RHIGH bit reads as 1 if the remote temperature has
exceeded the remote high limit and remains greater than
the remote high limit less the value in the Hysteresis
Register.
The LLOW and RLOW bits are not affected by the AL/TH
bit. The LLOW bit reads as 1 if the local low limit was
exceeded since the last clearing of the Status Register.
The RLOW bit reads as 1 if the remote low limit was
exceeded since the last clearing of the Status Register.
The values of the LLOW, RLOW, and OPEN (as well as
LHIGH and RHIGH when AL/TH is 0) are latched and will
read as 1 until the Status Register is read or a device reset
occurs. These bits are cleared by reading the Status
Register, provided that the condition causing the flag to be
set no longer exists. The values of BUSY, LTHRM, and
RTHRM (as well as LHIGH and RHIGH when AL/TH is 1)
are not latched and are not cleared by reading the Status
Register. They always indicate the current state, and are
updated appropriately at the end of the corresponding
ADC conversion. Clearing the Status Register bits does
not clear the state of the ALERT
pin; an SMBus alert
response address command must be used to clear the
ALERT
pin.
The TMP401 NORs LHIGH, LLOW, RHIGH, RLOW, and
OPEN, so a status change for any of these flags from 0
to 1 automatically causes the ALERT
pin to go low (only
applies when the ALERT
/THERM2
pin is configured for
ALERT mode).
Table 4. Status Register Format
STATUS REGISTER (Read = 02h, Write = NA)
BIT #
D7
D6
D5
D4
D3
D2
D1
D0
BIT NAME
BUSY
LHIGH
LLOW
RHIGH
RLOW
OPEN
RTHRM
LTHRM
POR VALUE
0
(1)
0
0
0
0
0
0
0
(1)
The BUSY bit will change to 1 almost immediately (<< 100祍) following power-up, as the TMP401 begins the first temperature conversion.
It will be high whenever the TMP401 is converting a temperature reading.