串行数字网络

摘要：本文提供了可以挂接两个或更多数字器件进行通信的串行接口的关键特性。设计工程师可以利用本文给出的表格对各种接口进行比较，根据具体的应用条件，如：信号线数、网络尺寸、速度、距离、抗干扰能力、故障容限和可靠性等，选择适当的接口标准。

Dallas Semiconductor提供1-Wire®串口协议，用于构建低成本、连线最少的方案。这种廉价的主/从结构可以利用其数字通信线提供从器件的电源。利用软件，通过微控制器单元(MCU)的一个I/O引脚即可构成1-Wire主机。我们还提供I²C、UART (RS-232)或USB至1-Wire的桥接电路，在远距离负载的应用中实现1-Wire通信协议，并对1-Wire波形进行优化。

	1-Wire	I²C	SMBus™	SPI™	MICROWIRE/PLUS™	M-Bus (EN1434)	CAN (ISO11898)	LIN Bus
Network Concept	single master, multiple slaves	multiple masters, multiple slaves	multiple masters, multiple slaves	single master, multiple slaves	single master, multiple slaves	single master, multiple slaves	multiple masters, multiple slaves	single master, multiple slaves
Number of Signal Lines	1 (IO)	2, (SCL, SDA)	2, (SMBCLK, SMBDAT)	4, (active-low CS, SI, SO, SCK)	4, (active-low CS, DI, DO, SK)	2 (lines can be swapped)	2 (CAN_H, CAN_L, terminated)	1 (LIN)
Optional signals	N/A	N/A	SMBSUS#, SMBALERT#	N/A	N/A	N/A	2nd GND, Power, Shield	N/A
Network Size	Up to 300 m (with suitable master circuit)	Limited by max. 400pF bus capacitance requirement	Limited by max. 400pF bus capacitance requirement	N/A (circuit board level)	N/A (circuit board level)	Max. 350m per segment of max. 250 slaves; max. 180nF	40m @1M bps1000m @ 50k bps (example)	Up to 40m, max. 10nF total load
Network Interface	open drain, resistive or active master pull-up	open drain, resistive or active master pull-up	open drain, resistive or active master pull-up	Push-pull with tristate	Push-pull with tristate	M to S: voltage drive S to M: current load	Differential open drain/source or open coll./emitter	open drain, resistive master pull-up
Network Voltage	From 2.8 to 6.0 V, device specific	From 1.8 to 5.5V, device specific	2.7V to 5.5V	From 1.8V to 5.5V, device specific	From 1.8V to 5.5V, device specific	~40V	VDD-VD (diode drop); ~4.5V max.	8 to 18V
Logic Thresholds	Vary with network voltage	Fixed level: >1.5V, >3.0 V VDD-related level: <30%, >70% of VDD	<0.8V, >2.1V	VDD-related level: <20% (30%), >70% of VDD (inconsistent)	Fixed level: <0.8V, >2.0V; VDD-related level: <20% (30%), >70% (80%) of VDD (inconsistent)	Master to slave: 24V, 36V nominalSlave to master: <1.5mA, >11mA	Differential: <50mV (recessive), >1.5V (dominant); driver specification	VDD-related level: <20%, >80% of VDD (driver spec.)<40%, >60% of VDD (receiver spec.)
Transmission	LS bit first, half-duplex	MS bit first plus Acknowledge bit, half-duplex	MS bit first plus Acknowledge bit, half-duplex	MS bit first, full-duplex	MS bit first, full-duplex	LS bit first, half-duplex, acknowledge response	MS bit first, half-duplex	LS bit first, half-duplex
Address Format	56 bits	7 bits, (10 bits defined but not implemented)	7 bits, (10 bits defined but not implemented)	N/A	N/A	8 bits (primary address), 64 bits (secondary address)	Message identifier 11 bits (standard format), 29 bits (extended format)	Message identifier 8 bits, including 2 parity bits
Network Inventory	Automatic, supports dynamic topology change	N/A; slave addresses hard-coded in firmware	ARP, Address Resolution Protocol (Rev. 2.0 only)	N/A; slave select (active-low CS) hard-coded in firmware	N/A; slave select (active-low CS) hard-coded in firmware	Automatic	N/A; message-based protocol, not address based	N/A; message-based protocol, not address based
Gross Data Rate	Standard: ~0 to 16.3k bps Overdrive: ~0 to 142k bps)	Standard: ~0 to 100k bps; Fast: ~0 to 400k bps; High-Speed: ~0 to 3.4M bps	10k to 100k bps	~0 to ~10 M bps (device specific)	~0 to ~5 M bps (device specific)	300, 2400, 9600 bps	~0 to 1M bps	~1k to ~20k bps
Access Time	Standard: ~ 5.4ms Overdrive: ~0.6ms (at maximum speed)	Standard: ~95µsFast: ~23µs(at maximum speed)	~95µs @ 100k bps	N/A	N/A	Primary address, 2400 bps: 13.75ms (short frame), 27.5ms (long frame)	At 1M bps 19µs (standard) or 39µs (extended) from start of frame to 1st data bit	At 20k bps 1.7ms from start of frame to 1st data bit
Data Protection	8-bit and 16-bit CRC	N/A	PEC Packet Error Code (Rev.1.1, 2.0)	N/A	N/A	Even parity, check sum, frames	15-bit CRC, frames, frame acknowledge	Check sum, frames
Collision Detection	Yes, through non-matching CRC	Yes (multi-master operation only)	Yes (Rev. 2.0 only)	N/A	N/A	Yes ("medium" and "strong" collisions)	Yes: CSMA/CD	Yes, through check sum
Slave supply	Parasitic (typical), VDD (exception)	VDD only	VDD only	VDD only	VDD only	Parasitic and/or local supply	VDD only, local or remote source	Parasitic only