Global Mixed-mode Technology Inc.
G781
If software standby command is received while a con-
version is in progress, the conversion cycle is trun-
cated, and the data from that conversion is not latched
into either temperature reading register. The previous
data is not changed and remains available.
Table 2. Temperature Data Format
(Two’s-Complement)
DIGITAL OUTPUT
DATA BITS
TEMP.
(°C)
SIGN
MSB
LSB
1111
1110
1001
0001
0000
0000
1111
1110
0110
1000
1111
EXT
111
011
100
110
100
001
111
111
100
110
000
Supply-current drain during the 125ms conversion
period is always about 320µA. Slowing down the con-
version rate reduces the average supply current (see
Typical Operating Characteristics). In between con-
versions, the instantaneous supply current is about
25µA due to the current consumed by the conversion
rate timer. In standby mode, supply current drops to
about 3µA. At very low supply voltages (under the
power-on-reset threshold), the supply current is higher
due to the address pin bias currents. It can be as high
as 100µA, depending on ADD0 and ADD1 settings.
+127.875
+126.375
+25.5
+1.75
+0.5
+0.125
-0.125
-1.125
-25.5
-55.25
-65.000
0
0
0
0
0
0
1
1
1
1
1
111
111
001
000
000
000
111
111
110
100
011
SMBus Digital Interface
From a software perspective, the G781 appears as a
set of byte-wide registers that contain temperature
data, alarm threshold values, or control bits, A stan-
dard SMBus 2-wire serial interface is used to read
temperature data and write control bits and alarm
threshold data.
Table 3. Extended Temperature Data Format
EXTENDED
DATA BITS
RESOLUTION
0.000°C
0.125°C
0.250°C
0.375°C
0.500°C
0.625°C
0.750°C
0.875°C
0000 0000
0010 0000
0100 0000
0110 0000
1000 0000
1010 0000
1100 0000
1110 0000
Each A/D channel within the device responds to the
same SMBus slave address for normal reads and
writes.
The G781 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 3). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data regis-
ter was previously selected by a Read Byte instruction.
Use caution with the shorter protocols in multi-master
systems, since a second master could overwrite the
command byte without informing the first master.
The temperature data format is 11bits plus sign in
twos-complement form for remote channel, with each
data bit representing 0.125°C (Table 2,Table 3),
transmitted MSB first.
Ver: 1.0
TEL: 886-3-5788833
http://www.gmt.com.tw
Oct 02, 2002
7
ETC [ ETC ]
