Các bác ơi, ai có tài liệu về NMEA 0183 truyền thông nối tiếp và chuẩn RS 485 cop lên em xem với, em

Các bác ơi, ai có tài liệu về NMEA 0183 truyền thông nối tiếp và chuẩn RS 485 cop lên em xem với, em cần lắm hu hu

Làm ơn giúp em với, gấp lắm rùi

for short) is a combined electrical and data specification for communication between marine electronic devices such as echo sounder, sonars, Anemometer (winds speed and direction), gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined by, and is controlled by, the US-based National Marine Electronics Association.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one "talker" to one "listener" at a time. Through the use of intermediate expanders, a talker can have a unidirectional conversation with multiple listeners, and using multiplexers, multiple sensors can talk to a single computer port. Third-party switches are available that can establish a primary and secondary talker, with automatic failover if the primary fails.
At the application layer, the standard also defines the contents of each sentence (message) type so that all listeners can parse messages accurately.
Electrical Characteristics (physical layer)
NMEA 0183 implementations vary, but can often interoperate with RS-232, RS-423, and RS-422. Each signal runs over a pair of wires. It is wise to test specific implementations for compatibility with these more widespread electrical standards, but, at the relatively slow speed of the interface, there is a high chance that it will work. Especially in a marine environment where grounding may be erratic, it can be wise to protect interfaces, especially of computer serial ports, with an optoisolator.
The official specification states that the "talker" drive circuit shall at minimum meet the requirements of EIA-422-A, a.k.a. RS-422. It also states that all "listeners" shall have optoisolators and other protective circuitry.
One frequently over-looked requirement for the "listener" portion of the circuit is the minimum level of operation. The "listener" must be able to operate with a minimum differential input voltage of 2.0 Volts and take no more than 2.0 mA current.
[e***] Serial Configuration (data link layer)
Baud Rate: 4800
Data Bits: 8
Parity: None
Stop Bits: 1 (or more)
[e***] Application Layer Protocol Rules
* Each message starting character is a dollar sign.
* The next first five characters identify the type of message (talker).
* All data fields that follow are comma-delimited.
* The first character that immediately follows the last data field character is an asterisk.
* The asterisk is immediately followed by a two-digit checksum representing a hex number. The checksum is the Exclusive OR of all characters between the ''$'' and ''*''. According to the official specification, the checksum is optional for most data sentences, but is compulsory for RMA, RMB, and RMC (among others).
* <CR><LF> ends the message.
Example of sentence:
Waypoint Arrival Alarm
$GPAAM,A,A,0.10,N,WPTNME*32
Where:
AAM Arrival Alarm
A Arrival circle entered
A Perpendicular passed
0.10 Circle radius
N Nautical miles
WPTNME Waypoint name
*32 Checksum data
A compound string from the NR203 GPS Receiver containing multiple messages. The actual messages decoded include?
* ZDA ?" Standard NMEA $..ZDA Time & Date message
* GLL ?" Standard NMEA $..GLL Geographic Position ?" Latitude/Longitude message
* NSV ?" NMEA message containing individual satellite information.
Typical ASCII String
$<CR><LF>
MRK,0<CR><LF>
ZDA,123336.8069,17,06,2001,13.0<CR><LF>
GLL,2924.11158,N,1211.07392,W, 75.97,M<CR><LF>
VTG,218.7,T,2.38,H,0.18,V<CR><LF>
SGD,-1.0,G,-1.0,M<CR><LF>
SYS,3T,9<CR><LF>
ZEV,0.28745E-006<CR><LF>
NSV,2,00,000,00,0.0,00.0,00,00,D<CR><LF>
NSV,7,00,000,00,0.0,00.0,00,00,D<CR><LF>
NSV,28,00,000,00,0.0,00.0,00,00,N<CR><LF>
NSV,1,00,000,00,0.0,00.0,00,00,D<CR><LF>
NSV,13,00,000,00,0.0,00.0,00,00,D<CR><LF>
NSV,4,00,000,00,0.0,00.0,00,00,N<CR><LF>
NSV,25,00,000,00,0.0,00.0,00,00,N<CR><LF>
NSV,0,00,000,00,0.0,00.0,00,00,N<CR><LF>
NSV,11,00,000,00,0.0,00.0,00,00,D<CR><LF>
NSV,0,00,000,00,0.0,00.0,00,00,N<CR><LF>
&
Description Form Field
Start Chars "$" 0
UTC of position fix ZDA,hhmmss.ssss,dd,mm,yyyy 1
Latitude in Degrees/Minutes llll.lllll 2
Direction of Lat (N or S) 3
Longitude in Degrees/Minutes yyyy.yyyyy 4
Direction of Lon (E or W) 5
Number of SVs NSV 6
Sat. i.d. number NSV,n,? 7
Repeated for ?on? sats
End Character ?o&?
The new standard, NMEA 2000, accommodates several "talkers" at a higher baud rate, without using a central hub.
The NMEA standard is proprietary and sells for at least US$ 270 as of August 2007. [1] However, much of it has been reverse-engineered from public sources and is available in references like gpsd, Glenn Baddeley''s and Dale DePriest''s.
[e***] Vendor extensions
Most GPS manufacturers include special messages to the standard NMEA set in their products for maintenance and diagnostics purposes. These extended messages are not standardized at all and are normally different from vendor to vendor.
[e***] Software Compatibility
NMEA 0183 GPS compliant software:
* NetStumbler
* Rand McNally StreetFinder
* Magic e-Map
* NemaTalker NMEA instrument simulation
[e***] See also
* ASCII
* Global Positioning System
* Serial communications
[e***] References
1. ^ Publications and Standards from the National Marine Electronics Association (NMEA) / NMEA 0183
[e***] External links
* National Marine Electronics Association
* NMEA''s website about NMEA 0183
* NMEA Protocol Conversion
* NMEA data information
nguồn: http://en.wikipedia.org/wiki/NMEA_0183

Bình chọn cho mình 5 sao nhé

RS485 (2-wire, half-duplex, differential, multi-drop (32 nodes), communications standard for distances up to 4000ft.)
The RS485 standard addresses the problem of data transmission, where a balanced (differential) transmission line is used in a multi-drop (party line) configuration (or point-to-point if only two devices are on the network). Up to 32-nodes (drivers and receivers) are allowed on one multi-drop, bi-directional network. Data rates of up to 10M bps are supported over short distances (40ft.). At the four-thousand foot distance limit, data rates of up to 100K bps are allowable. RS485 specifies a 2-wire, half-duplex communications bus. Because there are differences between RS485 and RS422(minor in many instances, except for loading [12K vs. 4K) many people refere to 4-wire RS485. While RS485 is a 2-wire standard, it does offer 32 nodes on a network, on the other hand RS422 (a 4-wire standard) only specifies up to 10 nodes. Therefore, while not technically correct, it does make some sence to refer to a 4-wire RS485 network that would extend the number of nodes on a 4-wire network to 32 standard loads.
The RS485 standard only specifies electrical characteristics of the driver and the receiver, it does not specify or recommend any protocol. Because matters of protocol are left to the user, it is often difficult (if not impossible) to connect RS485 devices from different manufacturers on the same network.
The RS485 standard allows the user to configure inexpensive local networks and multidrop communications links using twisted pair wire. A typical RS485 network can operate properly in the presence of reasonable ground differential voltages, withstand driver contentious situations, provide reliable communications in electrically noisy environments (good common mode rejection using twisted pair cable, shielding provides ad***ional protection), and support thirty-two or more (many IC manufacturers have 1/2, 1/4, 1/8 unit load devices) drivers and receivers on the line.
Twisted pair wire with a characteristic impedance of 120 ohms is recommended with 120 ohm termination at each end of the communications line. The common-mode voltage range is -7V to +12V. A driver in the high impedence (off) state is able to remain in this state over the common mode range, whether power is applied or not. The receiver is able to respond to differential signal levels of 200mV over the common mode range. The receiver load impedence is 12K ohms (or higher) and transmitter "leakage" current is ±100µA (or less) in either the powered or unpowered state. Unloaded driver output differential voltage can be as high as ±6V. Loaded driver voltage (32 nodes on the network and termination) should typically exceed ±1.5V.

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