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參數(shù)資料
| 型號： | DS87C550 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | EPROM High-Speed Micro with A/D and PWM(帶 A/D 和 PWM的EPROM/ROM高速微控制器) |
| 中文描述： | 存儲器高速微與A / D及PWM（帶A / D轉(zhuǎn)換和脈寬調(diào)制的存儲器/ ROM的高速微控制器） |
| 文件頁數(shù)： | 10/27頁 |
| 文件大?。?/td> | 119K |
| 代理商： | DS87C550 |
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APPLICATION NOTE 78
030998 10/27
CLOCK SOURCE CONTROL
Description
The DS87C5x0 incorporates a number of features to
control the clock source to the device. By controlling the
source of the system clock, the system designer can
simultaneously achieve higher performance and
decreased power consumption. To provide maximum
flexibility, the DS87C5x0 will operate from three clock
sources:
1. External Crystal (using internal crystal oscillator),
2. External Clock Oscillator,
3. Internal Ring Oscillator.
EXTERNAL CRYSTAL
The most common clocking source for the DS87C5x0 is
an external crystal. The DS87C5x0 incorporates a crys-
tal amplifier which is designed to drive industry standard
crystals over the operating range of the device. External
crystals provide a highly accurate clock source for tim-
ing–dependent peripherals such as internal timers and
serial ports, as well as device operation. The DS87C5x0
requires a fundamental–mode, parallel–resonant (also
called anti–resonant) AT cut crystal. Crystal oscillators
have significant start up times, however, which can
delay the operation of the device when powering on or
resuming from the Stop mode. The DS87C5x0 must
start operation with an external crystal or external clock
source after a power–on reset.
EXTERNAL CLOCK SOURCE
If a clock oscillator is already present in the system, it
can be used as the external clock source for the
DS87C5x0. External clock oscillators suffer from the
same start–up delays as the internal crystal oscillator,
and do not provide any special benefits. Either an exter-
nal crystal or external clock source can be used to clock
the device following a power–on reset or power–fail
reset.
RING OSCILLATOR
The ring oscillator is a low power digital oscillator inter-
nal to the DS87C5x0. It can be used as the primary sys-
tem clock, instead of an external crystal or clock oscilla-
tor, at any time except immediately following a
power–on reset. When enabled, it provides a 4 MHz
clock source for device operation. This is typically a
lower frequency than the system clock, and this pro-
vides a significant power savings. Once the device has
switched to the ring oscillator as the clock source, the
external crystal amplifier can be disabled, further reduc-
ing power consumption.
In addition, the ring oscillator eliminates the delay
associated with a crystal oscillator and provides an
almost instantaneous startup from Stop mode. When
used to restart the DS87C5x0 from Stop mode, the ring
oscillator will function for a minimum of 65,536 clock
cycles, at which time it can automatically switch to the
external crystal or continue to run from the ring oscilla-
tor. The ring oscillator cannot be used to clock the
device from a power–on state, however. Because the
ring oscillator does not exhibit as much stability as an
external clock, the DS87C5x0 should not perform timing
measurements or serial port data transfers while using
the ring oscillator as the clock source.
The ring oscillator finds wide applicability in applications
that only require sporadic bursts of processing. Such a
system will occasionally awaken from Stop mode, per-
form some activity, and then return to Stop mode. The
ring oscillator allows the system to quickly switch from
the lowest power state, perform an operation, and then
return to a low power state, without restarting a halted
external crystal. Figure 6 shows the advantages of
restarting from Stop mode with and without the ring
oscillator.
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| DS87C550-FCL | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:EPROM High-Speed Micro with A/D and PWM |
| DS87C550-FNL | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:EPROM High-Speed Micro with A/D and PWM |
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| DS87C550-QCL | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:EPROM High-Speed Micro with A/D and PWM |
| DS87C550-QCL+ | 功能描述:IC MCU EPROM ADC/PWM HS 68-PLCC RoHS:是 類別:集成電路 (IC) >> 嵌入式 - 微控制器， 系列:87C 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:260 系列:73S12xx 核心處理器:80515 芯體尺寸:8-位 速度:24MHz 連通性:I²C，智能卡，UART/USART，USB 外圍設(shè)備:LED，POR，WDT 輸入/輸出數(shù):9 程序存儲器容量:64KB（64K x 8） 程序存儲器類型:閃存 EEPROM 大小:- RAM 容量:2K x 8 電壓 - 電源 (Vcc/Vdd):2.7 V ~ 5.5 V 數(shù)據(jù)轉(zhuǎn)換器:- 振蕩器型:內(nèi)部 工作溫度:-40°C ~ 85°C 封裝/外殼:68-VFQFN 裸露焊盤 包裝:管件 |
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