MAX1617 Datasheet, PDF (12/20 Pages) ON Semiconductor – SMBus Temperature Sensor with Internal and External Diode Input

Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 4. Command-Byte Bit Assignments
REGISTER
RLTS
RRTE
RSL
RCL
RCRA
RLHN
RLLI
RRHI
RRLS
WCA
WCRW
WLHO
WLLM
WRHA
WRLN
OSHT
COMMAND
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
0Dh
0Eh
0Fh
POR STATE
0000 0000*
0000 0000*
N/A
0000 0000
0000 0010
0111 1111
1100 1001
0111 1111
1100 1001
N/A
N/A
N/A
N/A
N/A
N/A
N/A
FUNCTION
Read local temperature: returns latest temperature
Read remote temperature: returns latest temperature
Read status byte (flags, busy signal)
Read configuration byte
Read conversion rate byte
Read local T_HIGH limit
Read local T_LOW limit
Read remote T_HIGH limit
Read remote T_LOW limit
Write configuration byte
Write conversion rate byte
Write local T_HIGH limit
Write local T_LOW limit
Write remote T_HIGH limit
Write remote T_LOW limit
One-shot command (use send-byte format)
*If the device is in hardware standby mode at POR, both temperature registers read 0°C.
The Alert Response can activate several different slave
devices simultaneously, similar to the I²C General Call.
If more than one slave attempts to respond, bus arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERT line low
until serviced (implies that the host interrupt input is
level-sensitive). Successful reading of the alert
response address clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the various other registers within the
MAX1617. The register’s POR state is 0000 0000, so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current local temperature data.
The one-shot command immediately forces a new conver-
sion cycle to begin. In software standby mode
(RUN/STOP bit = high), a new conversion is begun, after
which the device returns to standby mode. If a conversion
is in progress when a one-shot command is received, the
command is ignored. If a one-shot command is received
in auto-convert mode (RUN/STOP bit = low) between con-
versions, a new conversion begins, the conversion rate
timer is reset, and the next automatic conversion takes
place after a full delay elapses.
Configuration Byte Functions
The configuration byte register (Table 5) is used to
mask (disable) interrupts and to put the device in soft-
ware standby mode. The lower six bits are internally set
to (XX1111), making them “don’t care” bits. Write zeros
to these bits. This register’s contents can be read back
over the serial interface.
Status Byte Functions
The status byte register (Table 6) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether or not the ADC is convert-
ing and whether there is an open circuit in the remote
diode DXP–DXN path. After POR, the normal state of all
the flag bits is zero, assuming none of the alarm condi-
tions are present. The status byte is cleared by any
successful read of the status byte, unless the fault per-
sists. Note that the ALERT interrupt latch is not auto-
matically cleared when the status flag bit is cleared.
When reading the status byte, you must check for inter-
nal bus collisions caused by asynchronous ADC timing,
or else disable the ADC prior to reading the status byte
(via the RUN/STOP bit in the configuration byte). In
one-shot mode, read the status byte only after the con-
version is complete, which is 150ms max after the one-
shot conversion is commanded.
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