As Ozee mentions, there is a serial port on the front of the controller. Use a null modem cable to connect from a serial port on your PC to the "Channel 0" port on the controller. If you don't have a real serial port on your PC, most USB/RS232 adapters work just fine.
A more expensive option is the 1784-U2DHP. This is the replacement for the PCMK which is no longer manufactured. The U2DHP is a USB to DH+ adapter. The benefit here is that if your devices are networked, the U2DHP would allow you to plug into and see/program/monitor any of those devices. The serial connection requires you to plug into the specific SLC controller with which you need to communicate. But the U2DHP is very expensive where a null modem cable is not.
OG