The AC500 is ABB's PLC version after the AC31 family of controllers specifically designed for factory automation. It is totally IEC 61131 level 3 compliant supporting all languages (IL, ST, LAD, SFC, CFC).
Siemens S7-300 is also very much designed for the same purpose - factory automation, special purpose machines, etc., but since the controller was engineered about 10 years ago and with Siemens not changing or upgrading its STEP 7 software, ease of use and configuration lies with the AC500 configuration tool CodeSys.
Siemens also doesn't support IL, and needs optional packages like GRAPH and SCL to be supported by IEC 61131.
CodeSys is a very flexible software tool for AC500 that allows ease of configuration and testing of programs though there isn't a great tool of cross references.
AC500 CPU PM581 also supports ethernet and Modbus, and comes preloaded with blocks for these protocols. Profibus needs an extra comm card CM572, where as Siemens PLC only supports Profibus and needs extra CPs and licenses for Modbus and ethernet connectivity. Also AC500 connection can be configured directly through ethernet or serially. You need to shell out extra money for a PC Adapter (MPI) to work an ES in case of Siemens. Both PLCs support distributed I/Os through Profibus.
On the whole, AC500 can be said to be very near a PAC, considering its ease of use, and S7-300 series will always have a lower hand when it comes to STEP 7.
i want to tell you that the new generation of SIEMENS PLC is mainly has profinet integrated in the CPU. so it do not need any type of PC adapter and it is easy to configure it and has wide range of HMI panels.
Sirs, please check the latest developments regarding usability, ease of use and efficiency of Siemens: http://www.engineering-redefined.com/ or www.tia-portal.com; which might be relevant to reevaluate the above mentioned comments. The Softwares Step7 and WinCC seem to have undergone significant changes since the launch of the TIA Portal framework.
Weak points of ABB AC500 PLCs in comparison with S7-300:
1-You must have the exact version of the on-line program to go on-line other wise you must do a full download. You can not upload the program.
2-You can not upload variables, you must save them to the RAM disc using RETAIN_SAVE PLC code and then export them to a SD card using RETAIN_EXPORT PLC code.
I would rather have old software that is fully featured than new software that has a lot of short comings.
