Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00
Summary:
Some protocols do not permit write to digital to be performed in a single operation. Citect protocol drivers overcome this limitation by reading the entire word, modify the appropriate bit in the word and writing it back to the PLC. This can be a potentially dangerous operation if the PLC is changing others bits in that word at the same time. 

Solution:
The following protocols perform read/modify/write when writing to digitals

ABKT2, ABEI2, FUJI, FUJIT and SIEMENS: When writing to any digitals.

CCM: When digitals to R, SP, QAB or to PLC with unexpanded IO (enabled by -u special option in ports form) or writing to CCM325.

OMRON: When writing digitals to IO relays, HR, LR and DM.

MELSEC: When writing digitals to TN, CN, D, W, R and D.

COMLI: When writing to L.

HWELL, UNITEL, MELSECF, KF, TELMAP, SINEC, GEMLAND and SIDIRECT

MODBUS and MBPLUS: Writes to bits in registers only. Normal digitals OK. See also Q2023.

vv 
Keywords:
 

Attachments