Siemens 880 Instruction Manual download pdf (Page 49)

6 Start-up 12.93

6.3 User data blocks

On each cold restart, certain data blocks are set up and written in ascending order into the

user data segment. A list of these data blocks is contained in the INTERFACE DESCRIPTION

PART 1: SIGNALS of the control concerned.

Data blocks DB 30 to DB 71 are defaulted with 0. The channel, spindle and axes data blocks

are defaulted with the user data if they are enabled for writing (see INTERFACE DESCRIP-

TION, PART 1: SIGNALS).

A warm restart has the same initialization as a cold restart except that

• User machine data (DB 62, DB 65) and

• Setting data (DB 68, DB 71)

are not defaulted with 0, but retain their values.

Note:

The decoding blocks for the NC channels (DB 80 and higher) are not set up or initialized by

the system.

6.4 Timeout analysis

A write access of the PLC to the communication or local bus is executed independently by the

bus interface. Write accesses are acknowledged immediately, and the PLC program can conti-

nue (Buffered access to communication/local bus). If a timeout occurs during such an access

the current state of the registers of the processor and co-processor give no information as to

the cause of the timeout.

The user can switch off buffered accesses to the communication and local bus (e.g. to test

STEP 5 programs during the installation phase) via machine data (PLC operating system MD

bit 6049.0). These accesses are then slower because the processor only receives an

acknowledgement when the whole bus cycle has finished.

Machine data 6049.0 must be set in order to be able to determine the exact cause of a

timeout.

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Siemens 880 Instruction Manual Page 49