Error handling and diagnostics
44
Embedded PC
Terminal Bus Analysis in PLC-Program
To analyze the terminal bus (K-Bus) the programmer can access the registers described in the architecture. The
access to the PLC-program is realized via TwinCAT. The registers are described in the architecture of the terminal
bus connectors (CX1100-000x.
For analysis four signals / variables are used:
•
BusState (describes the state of the bus: 0 -> no error, 1 -> bus error)
•
ErrorCode (same error code as the LED blink code)
•
ErrorArg (same argument code LED blink code)
•
Request[0] (output to request error codes / reset bus)
In the PLC program some external variables must be defined:
VAR
k_bus_request AT %QX0.0 : BOOL;
k_bus_err_code AT %IB0
: USINT;
k_bus_err_arg AT %IB1
: USINT;
k_bus_state AT %IB2
: USINT;
END_VAR
In the PLC program the analysis can be done as follows: (this is only pseudo code)
....
IF k_bus_state = 1 THEN
(* an error occured on K-Bus*)
k_bus_request := TRUE;
(* request vaules for ErrCode and ErrArg *)
CASE k_bus_err_code OF
0 : return;
(* should not happen, though an error occured *)
1 : CASE k_bus_arg OF
0 : report error;
(* EEPROM checksum error *)
1 : report error;
(* overflow in code buffer *)
2 : report error;
(* unknown datatype *)
END_CASE;
2 : CASE k_bus_arg OF
0 : report error;
(* programmed configuration, wrong table entry *)
ELSE report error;
(* wrong table entry *)
END_CASE;
3 : report error
(* K-Bus command error *)
4 : CASE k_bus_arg OF
0 : report error;
(* break after power supply *)
ELSE report error;
(* break after terminal 'k_bus_arg' *)
END_CASE;
5 : report error
(* K-Bus-error during register-communication with
terminal
'k_bus_arg'
*)
9 : CASE k_bus_arg OF
0 : report error; (* checksum error in program flash *)
ELSE report error;
(* terminal 'k_bus_arg' does not exist in boot
configuration
*)
