I had a R2E4. First of all I recommend getting a programming manual. Try machinemanuals.net or Ebay.
At first I used a Radio Shack TRS80 model 100 to upload download and edit with RS232.
Later I used a MAC running EZCAM (EZMILL) to generate programs and download.
I have also used PROCOMM for upload and download as well as editing in terminal mode (chat). It was a DOS shareware version. Similar to KERMIT.
Powerful editor and canned cycles.
Port A is used for upload, download and editing. Port B for EZLINK uploads/downloads and DNC.
Control can store more than one program but memory is limited. Most CAM systems have many extra lines of code. Typically I could consolidate a 8 page program to less than one using loops and macros.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)