SMA1
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 12 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 LSB right aligned protocol
“LSB right aligned” protocol allows to right 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 lead the data word. This
protocol can be used in sensors having any resolution. The word has a length of
25 bits.
The device uses 20 bits to provide the position information, unused bits (from
20 to 24) are set to 0 (zero).
Thus:
Model
Resolution Length of the word
Max. number of
information
SMA1-GA2-5-...
0.005 mm
25 bits
20 bits (1,048,575)
The output code of the sensor can be GRAY or BINARY (see the order code).
The length of each information is equal to the resolution (5 µm).
Position structure:
bit
24 … 20
19
…
0
value
00000
MSB
…
LSB
WARNING
The position value issued by the sensor is expressed in pulses; to convert the
pulses into a metric measuring unit you must multiply the number of detected
pulses by the resolution.
EXAMPLE
SMA1-GA2-5-…
resolution = 5 µm
detected pulses = 123
position value = 123 * 5 = 615 µm = 0.615 mm
MAN SMA1 E 2.9.odt
5 - SSI interface
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