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G771 Datasheet(PDF) 10 Page - Global Mixed-mode Technology Inc

Part No. G771
Description  Two Remote Temperature Sensors with SMBus Serial Interface and System Reset Circuit
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Maker  GMT [Global Mixed-mode Technology Inc]
Homepage  http://www.gmt.com.tw
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G771 Datasheet(HTML) 10 Page - Global Mixed-mode Technology Inc

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Ver: 0.2 Preliminary
Dec 11, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
10
G771
Global Mixed-mode Technology Inc.
If the remote channel is shorted (DXP to DXN or DXP
to GND), the ADC reads 0000 0000 so as not to trip
either the THIGH or TLOW alarms at their POR set-
tings. In applications that are never subjected to 0°C in
normal operation, a 0000 0000 result can be checked
to indicate a fault condition in which DXP is acciden-
tally short circuited. Similarly, if DXP is short circuited
to VCC, the ADC reads +127°C for both channels, and
the device alarms.
ALERT Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response ad-
dress. Interrupts are generated in response to THIGH
and TLOW comparisons and when the remote diode is
disconnected (for continuity fault detection). The in-
terrupt does not halt automatic conversions; new tem-
perature data continues to be available over the SMBus
interface after ALERT is asserted. The interrupt output
rupt output pin is open-drain so that device can share
a common interrupt line. The interrupt rate can never
exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see Alert Response Address section). Prior to taking
corrective action, always check to ensure that an in-
terrupt is valid by reading the current temperature.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (0001 100). Then
any slave device that generated an interrupt attempts to
identify itself by putting its own address on the bus.
Table 4. Command-Byte Bit Assignments
REGISTER
COMMAND
POR STATE
FUNCTION
RRTE2
00h
0000 0000b
Read 2nd remote temperature: returns latest temperature
RRTE1
01h
0000 0000b
Read 1st remote temperature: returns latest temperature
RSL
02h
N/A
Read status byte (flags, busy signal)
RCL
03h
0000 0000b
Read configuration byte
RCRA
04h
0000 0010b
Read conversion rate byte
RRHI2
05h
0111 1111b (127) Read 2nd remote THIGH limit
RRLS2
06h
1100 1001b(-55)
Read 2nd remote TLOW limit
RRHI1
07h
0111 1111b (127) Read 1st remote THIGH limit
RRLS1
08h
1100 1001b (-55) Read 1st remote TLOW limit
WCA
09h
N/A
Write configuration byte
WCRW
0Ah
N/A
Write conversion rate byte
WRHA2
0Bh
N/A
Write 2nd remote THIGH limit
WRLN2
0Ch
N/A
Write 2nd remote TLOW limit
WRHA1
0Dh
N/A
Write 1st remote THIGH limit
WRLN1
0Eh
N/A
Write 1st remote TLOW limit
OSHT
0Fh
N/A
One-shot command (use send-byte format)
TCRIT1
35h
0110 1100b (108)
Critical temperature for 1
st remote temperaure sensor
TCRIT2
36h
0101 1000b (88)
Critical temperature for 2
nd remote temperaure sensor
The Alert Response can activate several different slave
devices simultaneously, similar to the SMBus General
Call. If more than one slave attempts to respond, bus
arbitration 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 mas-
ter index that points to the various other registers
within the G771. 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
conversion 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 in auto-convert mode (RUN/STOP bit = low)
between conversions, a new conversion begins, the
conversion rate timer is reset, and the next automatic
conversion takes place after a full delay elapses.


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