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| 型号： | G771 |
| 厂商： | Global Mixed-mode Technology Inc. |
| 元件分类： | 温度/湿度传感器 |
| 英文描述： | Two Remote Temperature Sensors with SMBus Serial Interface and System Reset Circuit |
| 中文描述： | 两个远程温度传感器，带有SMBus串行接口和系统复位电路 |
| 文件页数： | 14/15页 |
| 文件大小： | 268K |
| 代理商： | G771 |
Ver 0.2 Preliminary
Dec 11, 2001
TEL: 886-3-5788833
http://www.gmt.com.tw
8
G771
Global Mixed-mode Technology Inc.
Interfacing to Ps with Bi-directional Reset Pins
A P with bi-directional reset pins (such as the Mo-
torola 68HC11 series) can connect to the G771 reset
output. If, for example, the G771 RESET output is
asserted high and the P wants to pull it low,
indeterminate logic levels may result. To correct this,
connect a 4.7k
resistor between the G771 RESET
output and the P reset I/O (Figure 4). Buffer the
G771 RESET output to other system components.
Benefits of Highly Accurate Reset Threshold
Most P supervisor Ics have reset threshold voltages
between 5% and 10% below the value of nominal sup-
ply voltages. This ensures a reset will not occur within
5% of the nominal supply, but will occur when the sup-
ply is 10% below nominal.
When using Ics rated at only the nominal supply ±5%
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
The G771 use highly accurate circuitry to ensure that
reset is asserted close to the 5% limit, and long before
the supply has declined to 10% below nominal.
Fig 3. RESET Valid to VCC = Ground Circuit
SMBus Digital Interface
From a software perspective, the G771 appears as a
set of byte-wide registers that contain temperature
data, alarm threshold values, fan speed data, or con-
trol bits, A standard SMBus 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. Each A/D and fan control
channel within the device responds to the same
SMBus slave address for normal reads and writes.
The G771 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 5). 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 over-write the
command byte without informing the first master.
The temperature data format is 7bits plus sign in
twos-complement form for each channel, with each
data bit representing 1°C (Table3), transmitted MSB
first. Measurements are offset by +1/2°C to minimize
internal rounding errors; for example, +99.6°C is re-
ported as +100°C.
Fig 4. Interfacing to Ps with Bi-directional Reset I/O
V
CC
G771
RESET
GND
R1
100k
V
CC
G771
RESET
GND
R1
100k
V
CC
G771
RESET
GND
BUFFER
RESET
GND
V
CC
P
4.7k
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
V
CC
G771
RESET
GND
BUFFER
RESET
GND
V
CC
P
4.7k
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
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