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Description of the DP Functions, Data, and Error Codes

DP Base Programming Interface for CP 5613/CP 5614

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C79000-G8976-C108-01

4.3.2 Reading the Diagnostic Data of a DP Slave

Consistent Reading of the Diagnostic Data

Each individual slave has a fixed data area in the process image of the

CP 5613/CP 5614 (for more information on the data format see Section 4.6).

To allow the diagnostic data of a slave to be read consistently, your user program

first locks this data area to prevent it being updated by the DP master, then

accesses the area, and releases it again. The program locks the area by writing the

slave number to a control register in the process image. The data area is released

again by writing the value DPR_DP_UNLOCK to the same register.

There is also a counter that counts the diagnostic data of the relevant slave.

Example of Consistent Reading of the Diagnostic Data

"p" is a pointer to the process image that your user program obtained with the

"DP_get_pointer" call. Then 200 bytes of the diagnostic data of slave no. 5 are

copied to a local buffer "buf":

/* Lock the diagnostic data area against updating */

p->ctr.D_lock_diag_slave_adr = 5;

/* Evaluate the counter */

count = p->pi.slave_diag[5].diag_count;

/* Copy current data */

memcpy(buf, &p->pi.slave_diag[5].data[0],

p->pi.slave_diag[5].diag_len);

/* Cancel lock again */

p->ctr.D_lock_diag_slave_adr = DPR_DP_UNLOCK;

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Siemens SIMATIC NET PROFIBUS Manual de servicio Pagina 146