SMRA - SSI and BiSS
transmission. The cycle ends at the last rising edge of the clock signal (
3
). This
means that up to n + 1 rising edges of the clock signals are required for each
data word transmission (where n is the bit resolution); for instance, a 13-bit
encoder needs 14 clock edges. If the number of clocks is greater than the
number of bits of the data word, then the system will send a zero (low logic
level signal) at each additional clock, zeros will either lead (LSB ALIGNED
protocol) or follow (MSB ALIGNED protocol) or lead and/or follow (TREE FORMAT
protocol) the data word. After the period Tm monoflop time, having a typical
duration of 16 µsec, calculated from the end of the clock signal transmission,
the encoder is then ready for the next transmission and therefore the data
signal is switched high.
The clock signal has a typical logic level of 5V, the same as the output signal
which has customarily a logic level of 5V in compliance with RS-422 standard.
The output code can be either Binary or Gray (see the order code).
5.2 MSB left aligned protocol
“MSB left aligned” protocol allows to left align the bits, beginning from MSB
(most significant bit) to LSB (least significant bit); LSB is then sent at the last
clock cycle. If the number of clock signals is higher than the data bits, then
unused bits are forced to logic level low (0) and follow the data word. This
protocol can be used in sensors having any resolution.
The word has a variable length according to resolution, as shown in the
following table.
Sensor model
Ring model
Length of
the word
Max. number of
information
SMRA-BG-x-06-...
SMRA-GG-x-06-...
MRA/130-64
13 bits
12 bits (4096 info/rev.)
SMRA-BG-x-07-...
SMRA-GG-x-07-...
MRA/130-64
14 bits
13 bits (8192 info/rev.)
SMRA-BG-x-08-...
SMRA-GG-x-08-...
MRA/130-64
15 bits
14 bits (16384 info/rev.)
The number of information per revolution results from:
2 to the power of resolution
*
number of ring poles
EXAMPLE
SMRA-GG-2-
08
-...:
resolution = 08;
MRA/130-
64
:
number of poles = 64.
Hence: 2
8
*
64 = 256
*
64 = 16,384 information per revolution
MAN SMRA SSI_BiSS E 1.2.odt
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