Technical Engineering Definitions
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

AMI [Alternate Mark Inversion] A zero is sent as a 0 while a one is sent as either a positive voltage or negative, which alternates. So a 1 is sent as one polarity and than the opposite polarity.

AMI Encoding
CMI Data Encoding

Bi-Phase Encoding Sends two bits, or a bit change for each level. A 1 is sent as a zero-one combination and a 0 is sent as a one-zero combination. Bi-phase encoding requires twice the bandwidth of NRZ-L encoding.

Bi-Phase Encoding
Bi-Phase Encoding

CDP [Conditional Diphase]. Seems to be another name for Differential Manchester encoding.

CMI Encoding Coded Mark Inversion doubles the data rate. A zero is sent as a low to high [01] transition, while a one is sent as either a one [1] or zero [0] depending on the previous state. If the previous state was high the one is sent as a zero [0], if it was low the one is sent as a one [1].

CMI Encoding of data
CMI Data Encoding

CSMA/CD (Carrier Sense Multiple Access/Collision Detection) A local area network access method in which contention between two or more stations is resolved by collision detection. When two stations transmit at the same time, they both stop and signal a collision has occurred. Each then tries again after waiting a predetermined time period. To avoid another collision, the stations involved each choose a random time interval to schedule the retransmission of the collided frame. To make sure that the collision is recognized, Ethernet requires that a station must continue transmitting until the 50 microsecond period has ended. If the station has less than 64 bytes of data to send, then it must pad the data by adding zeros at the end. Used with Ethernet.

CSMA/CS (Carrier Sense Multiple Access/Carrier Sense) A node listens to the bus for a predetermined amount of time before transmitting and waits until the talking node has completed transmission.

CSMA/CR (Carrier Sense Multiple Access/Collision Resolution) allows multiple devices to talk at once, a protocol determines which device receives priority.

Data-Strobe: An encoding scheme in which a sequence of data bits (and clock) is encoded as the original data bit sequence, together with another bit sequence (strobe) which changes state whenever the data bit sequence does not.

Disparity The difference between the number of 1's and 0's in a Transmission Character. A Transmission Character with more 1's than 0's is said to have positive running disparity. A Transmission Character with more 0's than 1's is said to have negative running disparity. A Transmission Character with an equal number of 1's and 0's is said to have neutral disparity.

Enhanced non-return-to-zero-level [E-NRZ-L]. The same as NRZ-L but with the addition of a parity bit to the data string. The bit will be high or low, depending on either even or odd parity being used.

EOF End of Frame delimiter. This Ordered Set is always the last Transmission Word of a Frame. It is used to indicate that a Frame has ended and indicates whether the Frame is valid or invalid.

Bit-Parallel Refers to a set of concurrent data bits present on a like number of signal lines used to carry information. Bit-parallel data bits may be acted upon concurrently as a group (byte) or independently as individual data bits.

Byte-Serial A sequence of bit-parallel data bytes used to carry information over a common bus.

HDB3 [High Density Bipolar 3] is a modified AMI code which uses both positive and negative polarity signals. The difference is that 4 consecutive zeros are not sent but modified to one four different patterns, so that a non-zero voltage level is transmitted. The string of 4 consecutive zeros in the code will be replaced by either 000-, 000+, +00+ or -00- depending on what was transmitted before. In the first string of zeros the last bit is changed 000V. The polarity of the V bit is the same as the previous non 0 voltage (opposite to a '1' bit which causes a V signal with an alternate voltage according to the previous one). The B bit B00V is again used to change the polarity, so 000V patterns are sent on odd occurrences of four zeros and B00V patterns are sent on even occurrences.

Manchester Encoding Manchester Encoding translates a '1' into a low to high transition [01], and a '0' is translated into a high to low transition [10]. Also called Biphase Code. Used with the Ethernet interface. More on Manchester Encoding

Manchester Encoding
Manchester Encoding

NRZ Encoding Non-return to zero encoding is used in slow speed synchronous and asynchronous transmission interfaces. With NRZ, a logic 1 bit is sent as a high value and a logic 0 bit is sent as a low value [really no encoding at all]. The receiver may lose synchronization when using NRZ to encode a synchronous link which may have long runs of consecutive bits with the same value [no changes in voltage]. Other problems with NRZ include; Data sequences containing the same number of 1's and 0's will produce a DC level, and NRZ requires a large bandwidth, from 0Hz [for a sequence containing only 1's or only 0's] to half of the data rate [for a sequence of 10101010].

"A type of 'null' encoding, where a logical 'zero' is represented by a particular line state, and a logical 'one' by another. In other words, there is no encoding, as distinct from RZ encoding." NRZ is used with RS-232 and CANbus.

NRZ Encoding
NRZ Encoding

There are other variations of NRZ encoding; which include:
NRZ-L: [Non-Return-to-Zero-Level]: Same as NRZ [except for the 1st bit]
NRZ-M [Non-Return-to-Zero-Mark (NRZ-M) Encoding]: The polarity of the signal changes when the incoming signal is a one. An incoming zero would not change the polarity of the signal.
NRZ-S [Non-Return-to-Zero-Space (NRZ-S) Encoding]: Works just like NRZ-M, except the signal changes when the incoming data signal is a zero, not when the signal is a one.
NRZ-C [Non-Return-to-Zero-Change Encoding]: Same as NRZ-L.
NRZI [Non-Return-to-Zero-Inverted Encoding]: A '0' is encoded as no change in the level. However a '1' is encoded depending on the current state of the line. If the current state is '0' [low] the '1' will be encoded as a high, if the current state is '1' [high] the '1' will be encoded as a low. Used with FDDI and USB for example.
Read more on NRZ Encoding.

NRZI Encoding
NRZI Encoding

PAM5x5, no information.

Return-To-Bias (RB) Encoding The RB encoding method uses magnetic tape that is pre-set to one of the two polarities (+ or -). This pre-sets the magnetic tape to all zeros. Digital ones are then recorded onto the magnetic tape by magnetizing the tape in the opposite polarity. After each one pulse, the tape returns to its original bias condition.

Return-To-Zero (RZ) Encoding The RZ encoding method sends a '0' level as 0 volts, and sends a '1' level as +volts [for the first half of the bit time] followed by 0 volts [for the second half of the bit time]. So a '0' is twice as long as '1', because a '1' is sent as a +v and then a 0v. If the data sequence is all high, then the pattern sent is 1,0,1,0 ... The frequency of the data rate for all an all high pattern defines the bandwidth.

Symbol A reformatted character. In the example Symbol format to the right, each symbol has three 1's and three 0's:

PC motherboard

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