Crc; Troubleshooting - Balluff BML-S1G0-B7-M5E-0-S284 Serie Betriebsanleitung

BML-S1G0-B/S7_ _-M5E_-_0-(SA26-)S284
Absolute Magnetically Coded Position Measuring System
6
Interfaces (continued)
With the first rising edge (trigger time), the controller
–
signals that it is requesting a value from the sensor
head. The position value valid at this point is included
in the data transmission later on.
– The sensor head confirms the data request with the
second rising edge of the clock by setting low on the
data line.
– The time difference between the second rising edge of
the clock and the first low of the sensor head data line
corresponds to the runtime of both signals. It appears
with all further frame edges and can thus be
compensated for in the controller. This makes it
possible to use much longer cables or higher data
rates than with SSI interfaces.
Example: Data with a Clk rate of 1 MHz can be
transmitted by e.g. up to 400 m. Only around 20 m
would be possible without runtime compensation.
– All further bits that the sensor transfers are output in
the sensor at the next rising edge.
– The sensor prepares the data during tbusy. Once this
is completed, the sensor will set the high (start bit) data
signal and then transfer the data. First the CDS bit, the
response or echo of the CDM bit that was sent by the
controller in the last frame, or the queried data is
output.
– Afterwards the data is transmitted starting with MSB
and going to LSB.
– An error bit and warning bit as well as the CRC follow.
– Register communication:
A bit can be transmitted by the controller to the sensor
head with each frame. To do this, the controller's clock
signal is either set to high or low during t
= 2 × t ). The sensor head recognizes it as a high or
Clk
low bit (CDM) and mirrors it in the CDS bit in the next
frame. As a result, the controller can detect if the bit
was recognized correctly (secure transmission).
– By transmitting one bit per frame, various addresses in
the sensor head can be read and written using several
frames. Further information on errors or warnings are
also available there. Customer data can also be saved
and read.
18 english
6.2.1
To ensure the integrity of the data, a cyclic redundancy
check (abbreviated CRC) is used in the controller. Here, a
check value is calculated for the transmitted data in both
the sensor and controller and then compared. If both
values are identical, the data has been transmitted
correctly. If they are different, the data has been
transmitted incorrectly and the position value must be
requested again.
The controller is parameterized as follows:
– 4 null bits
– Position (28 bits)
– 1 error bit
– 1 warning bit
– CRC: 6 bits (transferred inverted)
The counter polynomial for CRC determination is
0x43 (hex), 67 (dec) or 1000011 (bin).
6.2.2
Information on errors and warnings is available. The
position measuring system outputs a maximum of 8 errors
and 8 warnings. Regardless of the interface, the
16 messages are displayed through different colors (LED
off, red, orange) and LED flashing sequences (see
section 8 on page 27).
In the following, errors and warnings are referred to as EW
events.
If the BML detects an EW event, it makes a note of it and
transmits it with the error/warning bit once during the next
time (timeout
data query. At the same time, an LED flashing sequence
m
(see section 8 on page 27) is started. This flashing
sequence is output at least once until the data query has
taken place.
If the EW event is present for a longer period of time
across multiple data queries, the corresponding bit is set
and the LED flashing sequence output during each data
query.
If multiple EW events occur successively, the flashing
sequence changes accordingly.

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