Protocol analysis
R&S
®
RTE
731User Manual 1326.1032.02 ─ 20
SENT operates via a three wire connection, a signal line, a supply voltage line for the
sensor and a ground line. It transmits data digitally in variable timing units and evalu-
ates the time between two falling edges (single edges). The signal is amplitude modu-
lated with a constant amplitude voltage. Thus influences of interfering signals are not
critical.
SENT key features
Main characteristics of SENT are:
●
serial communication protocol
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3 wires: SENT (signal line), 5V (voltage line), GND (ground line)
●
output only, from sensor to receiver
●
point-to-point transmission, no bus
●
digital transmission
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high baud rate
●
data transmission in variable timing units of 4 bits (1 nibble) between two falling
edges
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transmitter-specific clock period (tick)
●
time measured between single falling edges
13.13.1.1 SENT transmission concept
A sensor converts the analog measured data to a digital signal, and thus transmits a
series of pulses to the receiver. The receiver, e.g. an ECU processes the received sig-
nal also digitally.
The format of a SENT message frame has a fixed pulse order and a transmitter-spe-
cific clock period. The total transmission time varies depending on the clock variation of
the transmitter and the transmitted data values. The data pulses embedded in the
transmission sequence represent one or multiple data parameters to be communica-
ted. The last pulses in a message frame are the CRC check pulse, allowing the
receiver to perform a number of diagnostic tests, and an optional pause pulse.
A SENT transmission starts without a request from the receiver. Consecutive sequen-
ces are transmitted continuously after the falling edge of the last pulse.
The SENT protocol distinguishes between two channel types:
●
Fast channel: transmits primary data, i.e. sensor readings like temperature, pres-
sure, mass air flow, throttle position.
●
Slow channel: transmits secondary data consisting of transfer characteristics, sen-
sor ID, type, manufacturer diagnostic, etc.
The slow channel transmission provides two serial message formats Short and
Enhanced for customizing the secondary data.
The data of both, the fast and the slow channels is transmitted simultaneously, by
including two bits of a slow channel message in the message frame of the fast chan-
nel. Even though it requires many fast channel messages to complete a slow channel
message, you can use this function to transmit several slow channel messages with
minimal impact on the primary sensor data and the data rate.
SENT (option R&S
RTE-K10)
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