Which type of Mitsubishi PLC are you talking about? The user manuals are normally a good place to start looking for information. You can download the manuals free of charge from Mitsubishi Electric's websites. The Q series PLC has an ASI module to version 2.11 and special configuration software for GX Developer (although you can configure the module without using the special software). We tend not to use ASI masters in the PLC chassis, instead we use gateway modules close to the ASI slaves (this means we don't have to worry about exceeding the cable length limit for ASI). There are CC-Link to ASI gateways, from several manufacturers, that work very well.