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參數(shù)資料
| 型號： | G768D |
| 英文描述： | ± 3oC remote thermal sensor with one fan control and SMBus interface.|Thermal Sensor / Detector Series |
| 中文描述： | ± 3oC遠(yuǎn)程溫度傳感器一個風(fēng)扇控制和SMBus接口。|熱傳感器/探測器系列 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大小： | 323K |
| 代理商： | G768D |
Ver: 1.4
May 23, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
9
G768D
Global Mixed-mode Technology Inc.
Ensuring a Valid Reset Output Down to V
CC
= 0V
When V
CC
falls below 1V, the G768D 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 μPs with Bi-directional Reset Pins
A μP with bi-directional reset pins (such as the Mo-
torola 68HC11 series) can connect to the G768D reset
output. If, for example, the G768D RESET output is
asserted high and the μP wants to pull it low, indeter-
minate logic levels may result. To correct this, connect
a 4.7k
resistor between the G768D RESET output
and the μP reset I/O (Figure 4). Buffer the G768D
RESET output to other system components.
Fig 3 RESET Valid to V
CC
= Ground Circuit
SMBus Digital Interface
From a software perspective, the G768D 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 G768D 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
G768D
RESET
GND
R1
100k
V
CC
G768D
RESET
GND
BUFFER
RESET
GND
V
CC
μP
4.7k
COMPONENTS
BUFFERED RESET
TO OTHER SYSTEM
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