Need basic info on 315-2DP CPU and TP-27 touch panel

This is presumably a very rudimentary set of questions but I have inherited some equipment that I need to add functionality to and have absolutely no documentation or s/w provided as basic tools to accomplish the task at hand.

The control panel that I intend to interfacesome external inputsto is controlled by a Siemens 315-2DP CPU w/ a variety of existing Siemens analog input modules and Siemens digital input and digital output modules. The human interface is accomplished by way of a Siemens TP-27 touch panel.

I've some PLC experience with TI/Koyo/PLCDirect systemsand althoughthat was a couple jobs and several years ago, I feel confident to tackle this as soon as I have the right tools.

Can someone help get me started here with helping to:
- locate necessary product documentation
- identify necessary s/w for communicating w/ the 315-2DP to view/edit the code, as well as where I might be able to get it (the cheaper the better)
- identify necessary s/w for communicating w/ the TP-27 to view/edit the code, as well as where I might be able to get it (the cheaper the better)

Thanks in advance for any assistance!