Ladder logic programing for PLC

["Zheng Lifang" <zhenglf@ssrc.ac.cn>]

Dear all,

I have been testing a Protecting System similar to APS's, which has three levels. The first is a VME crate plugged with a MVME2302/IOC, a SV2R6008 scanner. The second is a AB crate plugged with a 1771DCM, a PLC5/40, a 1771SDN and two I/O local modules. The third is a 1794ADN which controls a 1794IB16 & a 1794OB16.
The first success should contribute to much help from Prof.M.Kraimer, Dr.A Johnson and Dr. 

Now I meet some other questions. I use Rockwell RSlogix 4.11.00 revision to program PLC.

local input:    I:010
DCM read buf:   N10:0
DCM write buf:  N10:64
SDN read buf:   N11:0

When PLC sends data(block transfer) to DCM, the tag is set to 0 or 1 to distinguish the data from local I/O or from DeviceNet FlexI/O.

The rung orders are:
  
    copy I:010 to N10:66
    set N10:65=0  (tag=0)
    BTW to DCM (l=64)
    BTR read data to N11:0 from DeviceNet(l=62)
    copy N11:1 to N10:66
    set N10:65=1  (tag=1)
    BTW to DCM

I use DM2K to display and there occur two problems. 
1)Occasionally there is some exchanging data between local I/O and DeviceNet I/O. 
2)When I change the local or FlexI/O input module states, there is unbearable delay in DM2K to update. When I use .5second to process abDCM record, the delay is nearly 8 seconds.

Any suggestion is welcome.

Lifang