Hitachi SD.LINK User Manual page 90

The breakage of the primary ring and the secondary ring at different point
(different modules) as shown in Figure 5-12 could disable successful
communication. Never use the SD.LINK module in a situation like this.
Customers are advised to program all modules to detect a fault as soon as a
breakage occurs at an one point and report an alarm condition accordingly.
[Example] The CPL numbers of SD.LINK modules connected are 0 to 5 and the
RAS table starting address is set to RWF00 (YF70 is assigned as an
alarm reporting coil in the example below).
[S10mini]
RF00
RF05
RF40
RF45
NOTICE
[S10V]
RF00
RF05
RF40
YF70
RF45
5-13
5 PROGRAMMING
YF70