Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Mon, 01 Dec 2008 11:22:47 +0100

I have tested the s7plc driver (with the $(id):cmd_gap_pos_cmd record below) and
can confirm that nothing is sent to the PLC when the driver connects and no
output record processes.

If the receive buffer of the PLC is filled with zeros during connection, then it
is probably a problem of the PLC programming.

I can also confirm that exactly one buffer is sent to the PLC during iocInit
after the driver connects and the output records are initialized with PINI=YES.
This buffer does not contain uninitialized space (zeros) if all output records
have been processed with PINI=YES.

I also tested what happens if the PLC is started later than the IOC. The driver
connects and nothing is sent to the PLC until the first output record is
processed after connection.

Thus, I cannot find a bug in the driver.

Again, I strongly recommend to process every s7plc output record in the PINI
phase to ensure that the send buffer of the IOC does not contain uninitialized
zeros. One can use auto-save-and-restore to give values to the output records
before processing them in the PINI phase.

Dirk

Dirk Zimoch wrote:
> Hi,
> 
> This should not happen. I will check this. Please send me the configuration line
> from your startup script.
> 
> When no output record processes, nothing should be sent to the PLC. However, if
> some output records process and other output records have never processed, the
> unprocessed records send 0. For that reason, I suggest to process every S7plc
> output record at initialization with field(PINI,"YES"). The first package is
> sent to the PLC after all PINI records have finished.
> 
> Note that it is not possible to sent "half" buffers. When the IOC boots, the
> buffer is filled with 0. Whenever an output record processes, it writes to the
> buffer. Periodically, the driver checks if any output record has been processed.
> If yes, the whole buffer (including uninitialized parts) is sent to the PLC. If
> no, nothing is sent.
> 
> Dirk
> 
> Silver wrote:
>> hi, all:
>>
>>   I am using s7-plc driver written by Dirk, while I met a problem. while the driver connetcs to plc, it will clear the data buffer of PLC to zero. the database is like following:
>> record(ao,"$(id):cmd_gap_pos_cmd") 
>> {
>>     field(DESC,"command gap position")
>>     field(SCAN, "Passive")
>>     field(DTYP,"S7plc")
>>     field(OUT,"@Siemens_S7: 0/2 'T=UINT32'")
>>     field(LINR,"LINEAR")
>>     field(LOPR,0)
>>     field(HOPR,4294967295)
>>     field(EGUL,0)
>>     field(EGUF,429496.7295)
>>     field(DRVL,17.0000)
>>     field(DRVH,140.0000)
>>     field(EGU,"mm")	
>>     field(PREC,"4") 
>> }
>>   
>>   I remember the Passive mode will not write data to PLC when connecting, but why it can't work? Can anyone give some hints? thanks a lot for your help.
>>
>> Best regards
>> Geyang  2008-11-05
>>
>>
>>
> 

-- 
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System