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MAX1253/MAX1254
Stand-Alone, 10-Channel, 12-Bit System Monitors
with Internal Temperature Sensor and VDD Monitor
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19
Setup Register
The 8-bit setup register (Table 7) holds configuration
data common to all input channels. At power-up and
after a RESET command, this register defaults to
00000000b.
Setup Register: Sample Wait Bits (B7, B6, B5)
These 3 bits in the setup register (Table 8) set the wait
time between conversion scans. The following are
examples of how the MAX1253/MAX1254 begin a sam-
ple sequence (see the Setup Register: Reference
Selection Bits (B1, B0) section).
Operating in reference mode 00 (external reference for
voltage conversions, internal reference for temperature
conversions):
1) Convert the first-enabled channel. If this channel is a
temperature measurement, power up the internal ref-
erence (this takes 20s for each enabled tempera-
ture measurement in reference mode 00).
2) Sequence to the next-enabled channel until all chan-
nels have been converted.
3) Wait the sample wait period.
4) Repeat the procedure.
Operating in reference mode 01 (internal reference for all
conversions, can be powered down between scans):
1) Power up the internal reference, if powered down
(this takes 40s).
2) Convert the first-enabled channel, starting with the
internal temperature sensor, if enabled.
3) Sequence to the next-enabled channel until all
enabled channels have been converted.
4) Wait the sample wait time, and enter internal refer-
ence power-down mode if this period is greater than
80s.
5) Repeat the above steps.
Operating in reference mode 10 (internal reference for
all conversions, continuously powered up):
1) Convert the first-enabled channel.
2) Sequence to the next-enabled channel until all
enabled channels have been converted.
3) Wait the sample wait time.
4) Repeat the procedure.
Use the sample wait feature to reduce supply current
when measuring slow-changing analog signals. This
power savings occurs when reference mode 00 or 01 is
used in combination with wait times longer than 80s.
With reference mode 10 or wait times of less than 80s,
the internal reference system remains powered up, mini-
mizing any power savings. See the Computing Data
Throughput section. Table 8 shows the B7, B6, B5 wait
time encoding.
Setup Register: Interrupt Control (B4, B3)
Bits B3 and B4 in the setup register configure INT and
how it responds to an alarm event (see the Alarm
Register section). Table 9 shows the available INT
options.
Table 7. Setup Register Format
B7 (MSB)
B6
B5
B4
B3
B2
B1
B0 (LSB)
Sample wait bits
Interrupt
active
Interrupt
polarity
Scan
mode
Reference
source B1
Reference
source B2
Table 8. Wait Time Encoding
B7, B6, B5
WAIT TIME (ms)
000
0
001
0.080
010
0.395
011
1.310
100
4.970
101
19.600
110
78.200
111
312.000
Table 9. Interrupt Control
BIT FUNCTION
BIT
STATE
INT OPERATION
1
Driven high or low at all times
B4
Output
driver type
0
High-Z when inactive, driven (high
or low) when active
1Active = high, inactive = low or high-Z
B3
Output
polarity
0Active = low, inactive = high or high-Z