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9 CREATING A HARDWARE LOGIC
9.1 Main Blocks in the Hardware Logic Outline Window
Monoflop time
The monoflop time indicates the time set aside to refresh position data of the SSI encoder. The time is stipulated by an
encoder type. If the monoflop time is set to be shorter than the stipulated time, correct position data cannot be received.
When CLK transmission from the connected device is stopped by the monoflop time, the DATA signal from the SSI encoder
returns to High. This state indicates that the SSI encoder waits to start communication. At the timing the first fall of CLK from
this state is detected, position data is refreshed to the latest value. And then, at a rise of CLK, data transmission resumes in
order from the most significant bit.
With SSI communication specifications, after the receipt of the last bit of the receive frame, if CLK transmission resumes
before the encoder-wait-to-start-communication state is established, the position data of the previous receive frame is sent
from the encoder and received in the flexible high-speed I/O control module. In other words, if CLK transmission resumes
before the monoflop time elapsed, the latest position data is not latched in the encoder, and thus the latest position data
cannot be received in the flexible high-speed I/O control module.
Counting direction setting
Set the counting direction of received position data from the SSI encoder.
When "Direction" is set to "Reverse", the position data from the encoder is processed using the calculation formulas in the
table below.
Ex.
The following is the example of using the encoder with multi turn data length of 12 bits and encoder resolution of 4096 (= 12
bits) and counting in the addition direction.
Count value = (2
12
×
4096 - 1) - Position data = (2
24
- 1) - Position data
Encoder type
Calculation formula
Multi turn
Count value = (2
m
×
Encoder resolution - 1) - Position data
(m: Multi turn data length)
Single turn
Count value = (Encoder resolution - 1) - Position data
CLK
DATA
Most significant bit
Least significant bit
Monoflop
time
2
24
0
Count value
Count value when "Direction" is set to "Reverse"
Count value when "Direction" is set to "Forward"
Addition direction
Summary of Contents for MELSEC-L Series LD40PD01
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