RS422 - wire break and short-circuit detection (open circuit)

In the RS422 (differential input) modes it is possible to detect a wire break or short circuit at the individual encoder inputs.

In case of wire break, e.g. between input A and input A̅,

the differential voltage V_ID is almost 0 V,
which leads to an error with low differential voltage.

In case of a short circuit, e.g. between input A and input A̅, the error behavior is similar to a wire break and also leads to error detection.

Activation of error detection for each channel
Index (hex)	Name	Description
80n0:0B *	Error detection A	TRUE	Broken wire and short circuit detection for encoder input A enabled
80n0:0B *	Error detection A	FALSE	Broken wire and short circuit detection for encoder input A disabled
80n0:0C *	Error detection B	TRUE	Broken wire and short circuit detection for encoder input B enabled
80n0:0C *	Error detection B	FALSE	Broken wire and short circuit detection for encoder input B disabled
80n0:0D *	Error detection C	TRUE	Broken wire and short circuit detection for encoder input C enabled
80n0:0D *	Error detection C	FALSE	Broken wire and short circuit detection for encoder input C disabled
*) depending on the number of channels (n = 0 for channel 1 and n = 1 for channel 2)

Error detection using the example of a wire break or short circuit between inputs A and A̅.
Error diagnosis	Display	Description
LED A1	Green	A TRUE level is present
LED A1	Red	An error (open circuit) was detected
0x60n0:07 "Open circuit"	TRUE	Group error message for "Open circuit" A wire break or short circuit has occurred at one of the encoder inputs
0x60n0:07 "Open circuit"	FALSE	There is no "open circuit" error.
0x60n0:0F "TxPDO State"	TRUE	The position data are invalid.
0x60n0:0F "TxPDO State"	FALSE	The position data are valid.
0xA0n0:01 "Error A"	TRUE	An "open circuit" error (wire break or short circuit) has occurred at encoder input A.
0xA0n0:01 "Error A"	FALSE	There is no "open circuit" error.
DiagMessage (from FW02)	Text ID: 0x831B	Wire break or short circuit track A (channel n)

	Error bits not permanently set in case of wire break at an encoder input If a wire break is only present at one encoder input (e.g. only track A), it may happen in individual cases that the differential voltage (V_ID) is above the limit range (V_IDLow) due to the applied common mode voltage (V_CM). This means that the error is not clearly identified. The corresponding error bits ("Open circuit" and "Error A") are not permanently present!