12. ABSOLUTE POSITION DETECTION SYSTEM
12 - 19
1) The programmable controller turns on ABSM and SON at the leading edge of the internal servo-
on.
2) In response to ABS transfer mode, the servo detects and calculates the absolute position and
turns on ABST to notify the programmable controller that the servo is ready for data transmission.
3) After acknowledging that ABST is turned on, the programmable controller will turn on ABSR.
4) In response to ABSR, the servo outputs the lower 2 bits of the absolute position data and ABST
in the off state.
5) After acknowledging that ABST has been turned off, which implies that 2 bits of the absolute
position data have been transmitted, the programmable controller reads the lower 2 bits of the
absolute position data and then turns off ABSR.
6) The servo turns on ABST so that it can respond to the next request. Steps 3) to 6) are repeated
until 32-bit data and the 6-bit checksum have been transmitted.
7) After receiving of the checksum, the programmable controller confirms that the 19th ABST is
turned on, and then turns off ABSM. If ABSM is turned off during data transmission, ABSM is
interrupted and the [AL. E5 ABS time-out warning] occurs.
(c) Checksum
he checksum is the code which is used by the programmable controller to check for errors in the
received absolute position data. The 6-bit checksum is transmitted following the 32-bit absolute
position data.
At the programmable controller, calculate the sum of the received absolute position data using the
ladder program and compare it with the checksum code sent from the servo.
The method of calculating the checksum is shown. Every time the programmable controller receives
2 bits of absolute position data, it adds the data to obtain the sum of the received data. The
checksum is 6-bit data.
Example: absolute position data: -10 (FFFFFFF6H)
10
b
01
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
11
b
101101
b
- 10
FFFF FFF6
1111 1111 1111 0110
«Appendix»
Decimal
Hexadecimal
Binary
+
When the binary data of each 2bits of the absolute
position data is added up, "10 1101
b
" is obtained.
Therefore, the checksum of "-10" (absolute position data) is "2DH"
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