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參數(shù)資料
| 型號(hào)： | G768 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Remote/Local Temperature Sensor, 2 Fan Controllers with SMBus Serial Interface and System Reset Circuit |
| 中文描述： | 遠(yuǎn)程/本地溫度傳感器，2個(gè)風(fēng)扇，帶有SMBus串行接口和系統(tǒng)復(fù)位電路控制器 |
| 文件頁(yè)數(shù)： | 9/15頁(yè) |
| 文件大?。?/td> | 370K |
| 代理商： | G768 |
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Ver 1.3
Oct 28, 2002
TEL: 886-3-5788833
http://www.gmt.com.tw
9
G768B
Global Mixed-mode Technology Inc.
Ensuring a Valid Reset Output Down to V
CC
= 0V
When V
CC
falls below 1V, the G768B RESET output
no longer sinks current-it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to RESET can drift to undetermined voltages.
This presents no problem in most applications, since
most μP and other circuitry is inoperative with V
CC
be-
low 1V. However, in applications where RESET must
be valid down to 0V, adding a pull-down resistor to
RESET causes any stray leakage currents to flow to
ground, holding RESET low (Figure 3). R1's value is
not critical; 100k
is large enough not to load
RESET and small enough to pull RESET to ground.
Interfacing to Ps with Bi-directional Reset Pins
Ps with bi-directional reset pins (such as the Motorola
68HC11 series) can connect to the G768B reset out-
put. If, for example, the G768B RESET output is as-
serted high and the μP wants to pull it low, indetermi-
nate logic levels may result. To correct this, connect a
4.7k
resistor between the G768B RESET output
and the μP reset I/O (Figure 4). Buffer the G768B
RESET output to other system components.
Benefits of Highly Accurate Reset Threshold
Most μP 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 G768B 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 V
CC
= Ground Circuit
SMBus Digital Interface
From a software perspective, the G768B 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 G768B 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 μPs with Bi-directional Reset I/O
V
CC
G768B
RESET
GND
100k
R1
V
CC
G768B
RESET
GND
BUFFER
RESET
GND
V
CC
μP
4.7k
COMPONENTS
BUFFERED RESET
TO OTHER SYSTEM
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