LD25x
With Master operation, therefore other settings will result in generation of the
next upper or lower value according to above list. With all settings <250.0 kHz
the error between set rate and generated rate becomes negligible.
It is mandatory to set the baud rate also with “Slave” operation. In this case,
however, the setting is only used to determine the pause time for correct
synchronization (pause is detected after 4 clock cycles). The unit automatically
synchronizes with every remote clock signal within the specified baud rate
range.
8.2 Evaluation of encoder bits
This section is meant to explain the correlation between the basic parameter
bitS
(section “7.1 Basic settings” on page 14) and the operational parameters
Hi
bit
and
Lo bit
(see section “7.2 Operational parameters” on page 16). The
example below assumes that the encoder has a 16-bit resolution.
NOTE
Unused bits may be blanked out according to individual need.
Whenever the number of bits (clock cycles) requested from the SSI Master is
higher than the real number of encoder bits, all excessive bits must be
blanked by corresponding setting of parameters
Hi bit
and
Lo bit
(see
section “7.2 Operational parameters” on page 16).
8.2.1 Basic settings
In general, parameter
bitS
will always be set according to the real resolution of
the encoder (i.e.
bitS
= 16 with a 16-bit encoder). In this normal case the SSI
telegram will not contain any excessive bits.
With some applications (e.g. with Slave operation) however it may happen that
the Master transmits more clock cycles than the number of encoder bits (e.g. 21
clocks with a 16-bit encoder). In such a case the master would always request
21 bits from the encoder, where the encoder responds with 16 usable bits only,
followed by 5 waste bits. These 5 excessive bits must be blanked.
All standard SSI telegrams start with the most significant bit (MSB) and close
with the least significant bit (LSB). Unusable waste bits (X) will follow at the end
of the string. To blank these bits out, in our example we would have to set
Hi
bit
to 21 and
Lo bit
to 6 for proper evaluation of the encoder information.
H
i B
it
Lo
B
it
Requested
bits (clocks)
21
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
9 8 7
6
5 4 3 2 1
Usable bits
(encoder)
16
1
5
1
4
1
3
1
2
1
1
1
0
9
8
7
6
5
4 3 2
1
X X X X X
MAN LD25x E 1.0.odt
Hints for application
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