Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00 4.00
Summary:
I would like to setup redundant paths to my PLC but for whatever reason I want to use two different protocols, is this possible? 

Solution:
Citect may have several different protocols for one particular PLC. Officially Citect only supports redundancy when you use exactly the same protocol for the Primary and Standby links. In some cases you may want to use a different protocol for the Standby, for example one might be Ethernet and the other might be serial. Citect does not officialy support this configuration however if the datatype definition fro each of the two protocols in Citect are the same then it will work. Following is a section of the PROTDIR.DBF from the Citect BIN directory, if two protocols use the same specification file, eg. ABEI5 and KT5 then they will be compatible for redundancy.
 
TAG FILE BIT_BLOCK MAX_LENGTH OPTIONS
ABEI2 AB_2 640 1824 0x37f
ABEI250 AB250 912 1824 0x37f
ABEI3 AB3 912 1824 0x37f
ABEI5 AB5 912 1824 0x37f
KE2 AB_2 640 1920 0x37f
KE250 AB250 640 1920 0x37f
KE3 AB3 640 1920 0x37f
KE5 AB5 640 1920 0x37f
KF ABSLC 640 640 0x1ff
KT250 AB250 1536 1920 0x37f
KT3 AB3 1536 1920 0x37f
KT5 AB5 1536 1920 0x37f

(The PROTDIR.DBF contains a list of all the protocols, specifies some options for the protocol and references a specification file. There is a specification file for each protocol, this file species ranges and syntax for each data type supported by the protocol.. These files are all dBase III files.)

TAG FILE BIT_BLOCK MAX_LENGTH OPTIONS
TIDIRECT TIDIRECT 160 240 0x14f
TINEC TIWAY 2048 2048 0x14f
TISERIAL TIWAY 688 2048 0x14f
TIWAY TIWAY 512 2048 0x14f

If the two protocols do not use the same file then they may still be compatible. First the MAX_LENGTH field must be the same for both protocols. This specifies the maximum read size from the PLC. However if they are different you can reduce the protocol with the larger number to the same as the smaller number. This will reduce the performance of the driver, however it will allow the redundancy to be used.

For example with the TIWAY and TIDIRECT have a different MAX_LENGTH. If you change the TIWAY maximum length to 240 it will make the maximum read size the same for both protocols. This maximum length size is the size that a Citect client will ask for data over the network to the I/O server. The I/O Server will still optimise all the data requests and read from the TIWAY protocol with the real maximum read size of 2048. By decreasing the MAX_LENGTH you will force the Citect client to send more requests over the network cause a slight degrade in performance.

Also you must also check if each data type are the same, eg. Following are extracts from the TIDIRECT and TIWAY protocol specification files.

TIDIRECT.DBF

TEMPLATE UNIT_TYPE RAW_TYPE BIT_WIDTH LOW HIGH COMMENT
V%U 1 1 16 1 32767 Variable
X%U 6 0 1 1 32767 Discrete Input
Y%U 7 0 1 1 32767 Discrete Output
C%U 8 0 1 1 32767 Control
WX%U 9 1 16 1 32767 Packed Discrete Input
WY%U 0xa 1 16 1 32767 Packed Discrete Output
TCP%U 0xe 1 16 1 32767 Timer Counter Preset
TCC%U 0xf 1 16 1 32767 Timer Counter Current
LKC%L20 0x1000 2 32 0 64 Loop Gain
LTI%L21 0x1000 2 32 0 64 Loop Reset Time (minutes)

TIWAY.DBF

TEMPLATE UNIT_TYPE RAW_TYPE BIT_WIDTH LOW HIGH COMMENT
V%U 1 1 16 1 32767 Variable
X%U 6 0 1 1 32767 Discrete Input
Y%U 7 0 1 1 32767 Discrete Output
C%U 8 0 1 1 32767 Control
WX%U 9 1 16 1 32767 Packed Discrete Input
WY%U 0xa 1 16 1 32767 Packed Discrete Output
TCP%U 0xe 1 16 1 32767 Timer Counter Preset
TCC%U 0xf 1 16 1 32767 Timer Counter Current
LKC%U 0x60 2 32 1 64 Loop Gain
LTI%U 0x61 2 32 1 64 Loop Reset Time (minutes)

As you can see the specification for types V, X, Y, C, WX, WY, TCP and TCC are the same in both files, this means that you would use Tiway and TIDirect as a redundant pair for these types but if you were to use types LKC or LTI then it would not work because the protocol addressing for these is different. These types are not supported for redundancy between these two protocols

 
Keywords:
 

Attachments