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TLE5014
GMR-Based Angle Sensor
SICI
6
SICI
6.1
Basic Functionality
The SICI interface (SICI: Single-Wire Interface for Calibration and Inspection) is a one-wire programming
interface that allows read and write access to the working registers and EEPROM registers of the sensor. It is
bidirectional for every transferred bit, meaning that for every single bit sent by the master one bit is
immediately sent back from the slave. The speed of the interface is automatically determined from the length
of the first bit sent by the master.
The one-wire interface enables a robust data transmission at a speed of up to 240 kbit/s. It is a voltage
interface based on a bit-wise pulse-width-modulation (PWM) principle and requires an open-drain driver on
micro controller side. Regardless of the interface configuration of the TLE5014, the SICI interface is always
available on the IFB pin during the startup time.
In order to use the SICI interface, sensor and micro controller have to use an open drain output, so they can
actively pull a "low" level. The communication line has to be connected to V
1.5-2 kΩ. Higher values for the pull-up resistor may lead to problems to achieve the necessary speed of the
communication.
6.2
SICI Data Transfer
The communication via the SICI interface is based on transmitting a single bit to the sensor and immediately
receiving a bit. These bits form a 16-bit word. It makes the interface bit-synchronous, robust and very flexible
in timing. Bidirectional data transmission can thus be realized using only a single wire without a trimmed
oscillator on sensor or master side. To enhance the robustness of the interface, the sensor repeats the 16-bit
command word sent by the master in order to have a confirmation of the correct understanding of the
message, and transmits a safety word after each communication. Additionally, a time-out feature is
implemented: If during a communication the sensor does not receive a bit from the master within a certain
time span (see
Table
11, Interface reset time), the interface is reset and a new command can be sent.
6.2.1
Bit Encoding
For the SICI interface, bits are encoded as the difference in duration of consecutive "low" and "high" levels. To
transmit a bit to the sensor, the master sends one single low/high PWM signal with a period T, then pulls the
line to "low" again for a short time T
"low" and "high" time:
•
to transmit a "0" to the sensor, the master pulls the line "low" for a short time T
for a long time T - T
1
•
to transmit a "1" to the sensor, the master pulls the line "low" for a long time T
for a short time T - T
2
The sensor recognizes the total bit-time interval T as the duration between two consecutive falling edges from
the master. This encoding scheme is illustrated in
User's Manual
. The logic value of the bit is then encoded as the difference between
3
(typically T
= 0.3 * T)
1
(typically T
= 0.7 * T)
2
Figure
6.
31
by a pull-up resistor of approx.
DD
, then releases it to "high"
1
, then releases it to "high"
2
Rev. 1.0
2019-03-12
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