Many of the MODBUS features are initiated or Handshaked by Setting and Clearing Coils(Bits) in the PLC.

In order to improve the troubleshooting capability when features are not working we have added Diagnostics to the XL to show the Coils(Bits), we call them Function Coils, as the XL sees them.

The diagnostics are accessed in the PLC Communications screen by pressing the F3-More Data key until the Screen data heading changes from "Configuration Data" to "Diagnistics. The coils are shown in 8 bit( 1 Byte) groupings. If bit 0 is ON within a group, the group will show a '0' for the first bit. Otherwise, it will show a '-' for the first bit. If bit 7 is ON the group will show '7' for the last bit. Each group has a heading showing the upper and lower coil number within the range. You can determine which coils are ON by adding the individual bit number to the lowest coil number shown in the group header. For example: If the group header is 15-8 and the group shows "-6----1-" then Function Coils 9 and 14 are ON.

In important detail to know about the screen is that it shows the state of the coils as read out of the PLC. If the XL turns on a coil that is imeadiately turned back off by the PLC, that coil will never show up in the screen as ON because it will get cleared before the XL can read it.