Applies To:
  • CitectSCADA 5.xx

Is there a driver for a direct serial connection to Square D PLCs? What are it's limitations?

The Citect SQDIRECT driver supports a direct serial connection with Square D PLCs, and uses a protocol that was designed for use with Square D's SFI510 Sy/Link card. This protocol has specific timing requirements that the SFI510 card was designed to handle. The SQDIRECT driver must observe these timing requirements without the use of the SFI510 card. Under certain conditions, such as high CPU loading, the SQDIRECT driver may fail to meet these timing requirements and communications may fail.

It is recommended when using this driver that the system designer take note of the following recommendations:

  1. The Citect I/O Server should be a lightly loaded, high performance computer (as a rough indication, use a Pentium II 200MHz PC or better).
  2. The Citect I/O Server should not be a file server, and ideally not a Display Client.
  3. The integrator / customer should perform significant testing on the driver to ensure that the system will operate as desired.

CIT are looking at mechanisms to improve the stability of the driver with respect to meeting these timing requirements. This KB article will be updated accordingly when this occurs.

See also Q2305.