NMEA0183 is based on RS-422. The electrical
RS-422StandardEIA RS-422Physical MediaTwisted PairNetwork TopologyPoint-to-point, Multi-droppedMaximum Devices10 (1 driver & 10 receivers)Maximum Distance1500 metres (4,900 ft)Mode of OperationDifferentialMaximum Baud Rate100 kbit/s – 10 Mbit/sVoltage Levels−6V to +6V (maximum differential Voltage)Mark (1)Negative VoltagesSpace (0)Positive voltagesAvailable SignalsTx+, Tx-, Rx+, Rx- (Full Duplex)Connector typesNot specified
Typical Baud rate
4800Data bits8ParityNoneStop bits1HandshakeNone
USB is a horse of an entirely different color:
"USB allows the following signaling rates
. The terms speed
are used interchangeably. "high-" is alternatively written as "hi-".
- A low-speed (USB 1.0) rate of 1.5 Mbit/s is defined by USB 1.0. It is very similar to full-bandwidth operation except each bit takes 8 times as long to transmit. It is intended primarily to save cost in low-bandwidth human interface devices (HID) such as keyboards, mice, and joysticks.
- The full-speed (USB 1.1) rate of 12 Mbit/s is the basic USB data rate defined by USB 1.0. All USB hubs can operate at this speed.
- A high-speed (USB 2.0) rate of 480 Mbit/s was introduced in 2001. All hi-speed devices are capable of falling back to full-bandwidth operation if necessary; i.e., they are backward compatible with USB 1.1. Connectors are identical for USB 2.0 and USB 1.x.
- A SuperSpeed (USB 3.0) rate of 5.0 Gbit/s. The written USB 3.0 specification was released by Intel and partners in August 2008. The first USB 3 controller chips were sampled by NEC May 2009 and products using the 3.0 specification arrived beginning in January 2010. USB 3.0 connectors are generally backwards compatible, but include new wiring and full duplex operation.
"USB signals are transmitted on a twisted-pair
data cable with 90Ω
±15% characteristic impedance
labeled D+ and D−. Prior to USB 3.0, these collectively use half-duplex differential signaling
to reduce the effects of electromagnetic noise
on longer lines. Transmitted signal levels are 0.0 to 0.3 volts
for low and 2.8 to 3.6 volts
for high in full-bandwidth and low-bandwidth modes, and −10 to 10 mV for low and 360 to 440 mV for high in hi-bandwidth mode. In FS mode, the cable wires are not terminated, but the HS mode has termination
of 45 Ω to ground, or 90 Ω differential to match the data cable impedance, reducing interference
due to signal reflections
. USB 3.0 introduces two additional pairs of shielded twisted wire and new, mostly interoperable contacts in USB 3.0 cables
, for them. They permit
the higher data rate, and full duplex operation.
"A USB connection is always between a host or hub at the "A" connector end, and a device or hub's "upstream" port at the other end. Originally, this was a "B" connector, preventing erroneous loop connections, but additional upstream connectors were specified, and some cable vendors designed and sold cables
that permitted erroneous connections (and potential damage to circuitry). USB interconnections are not as fool-proof or as simple as originally intended.
The host includes 15 kΩ pull-down resistors on each data line. When no device is connected, this pulls both data lines low into the so-called "single-ended zero" state (SE0 in the USB documentation), and indicates a reset or disconnected connection.
"A USB device pulls one of the data lines high with a 1.5 kΩ resistor. This overpowers one of the pull-down resistors in the host and leaves the data lines in an idle state called "J". For USB 1.x, the choice of data line indicates of what signal rates the device is capable; full-bandwidth devices pull D+ high, while low-bandwidth devices pull D− high.
"Example of a Negative Acknowledge packet transmitted by USB 1.1 Full-speed device when there is no more data to read. It consists of the following fields: clock synchronization byte, type of packet and end of packet. Data packets would have more information between the type of packet and end of packet.
"USB data is transmitted by toggling the data lines between the J state and the opposite K state. USB encodes data using the NRZI line coding
; a 0 bit is transmitted by toggling the data lines from J to K or vice-versa, while a 1 bit is transmitted by leaving the data lines as-is. To ensure a minimum density of signal transitions remains in the bitstream
, USB uses bit stuffing
; an extra 0 bit is inserted into the data stream after any appearance of six consecutive 1 bits. Seven consecutive received 1 bits is always an error. USB 3.0 has introduced additional data transmission
A USB packet begins with an 8-bit synchronization sequence '00000001'. That is, after the initial idle state J, the data lines toggle KJKJKJKK. The final 1 bit (repeated K state) marks the end of the sync pattern and the beginning of the USB frame. For high bandwidth USB, the packet begins with a 32-bit synchronization sequence.
"A USB packet's end, called EOP (end-of-packet), is indicated by the transmitter driving 2 bit times of SE0 (D+ and D− both below max) and 1 bit time of J state. After this, the transmitter ceases to drive the D+/D− lines and the aforementioned pull up resistors hold it in the J (idle) state. Sometimes skew due to hubs can add as much as one bit time before the SE0 of the end of packet. This extra bit can also result in a "bit stuff violation" if the six bits before it in the CRC are '1's. This bit should be ignored by receiver.
A USB bus is reset using a prolonged (10 to 20 milliseconds) SE0 signal.
USB 2.0 devices use a special protocol during reset, called "chirping", to negotiate the high bandwidth mode with the host/hub. A device that is HS capable first connects as an FS device (D+ pulled high), but upon receiving a USB RESET (both D+ and D− driven LOW by host for 10 to 20 ms) it pulls the D− line high, known as chirp K. This indicates to the host that the device is high bandwidth. If the host/hub is also HS capable, it chirps (returns alternating J and K states on D− and D+ lines) letting the device know that the hub operates at high bandwidth. The device has to receive at least three sets of KJ chirps before it changes to high bandwidth terminations and begins high bandwidth signaling. Because USB 3.0 uses wiring
separate and additional to that used by USB 2.0 and USB 1.x, such bandwidth negotiation is not required."
Universal Serial Bus - Wikipedia, the free encyclopedia
No way can an RS422 device understand a USB device.