Siemens V3 Diagnostics via AS-Interface 7

ASIMON V3 - Configuration software for AS-Interface safety monitor

Programming and Operating Manual, Edition 09/2008, GWA 4NEB 333 1558 02 DS 02 163

Diagnostics via AS-Interface 7

Diagnostics via AS-Interface

Using the AS-Interface bus, diagnosis of the AS-Interface safety monitor and configured de-

vices is possible from the AS-Interface master, normally a PLC with master module.

However, to ensure reliable transmission and efficient evaluation of the diagnostic data, a

series of requirements must be satisfied:

• Relatively long telegram propagation times may occur, particularly when using an additio-

nal bus system between PLC and AS-Interface. Owing to the asynchronous transmission

in the master in the case of two successive, identical data calls, the PLC may not neces-

sarily know when the AS-Interface safety monitor is responding to the new call. Thus, the

answers to two successive, different data calls should differ by at least one bit.

• The diagnostic data must be consistent, i.e. the status information sent by the AS-Interface

safety monitor must match the actual device states, especially if the propagation time to

the PLC is longer than the updating time in the AS-Interface safety monitor

(approx. 30 … 150ms).

• Whether a deactivated relay of an output circuit represents the normal state depends on

the operating mode of the AS-Interface safety monitor. The diagnostics in the PLC should

only be called in the event of a deviation from the normal state.

The diagnostic procedure described below satisfies these requirements and should therefore

always be followed.

The PLC always queries the AS-Interface safety monitor alternately with two data calls (0) and

(1). These data calls return the basic information (state of the output circuits, protective/confi-

guration operation) to allow a diagnosis. The AS-Interface safety monitor answers the two calls

with the same user data (3 bit, D2 … D0). Bit D3 is a control bit, similar (but not identical) to a

toggle bit. D3 is 0 for all even data calls (0); D3 is 1 for all odd data calls (1). This enables the

PLC to detect whether the answer has changed.

Data calls (0) and (1) return the answer X000 if the normal state exists (protective operation,

everything OK). For devices with only one output circuit and with two dependent output circuits,

output circuit 2 is always marked as OK. With two independent output circuits, an unconfigured

circuit is also marked as OK. In order to be able to interpret what is OK and what is not OK, the

user must be familiar with his configuration.

Note

The assignment of an AS-Interface slave address for the AS-Interface safety monitor is a

prerequisite for diagnosing the AS-Interface safety monitor on the AS-Interface master.