[cctalk] DLOAD BASIC command for Color Computer 1/2 heritage

Over at the CoCo Mailing List, there's a archeological discussion about the DLOAD BASIC command in older versions of the Color Computer BASIC. It uses the serial port (and no doubt was designed for computer sharing in classrooms or similar), but the questions are around how it was designed and what inspiration is drew from. I infer MS wrote the code, and the protocol includes: P.ACK - Acknowledge - C8 hex. P.ABRT - Abort - BC hex. P.BLKR - Block request - 97 hex. P.FILR - File request - 8A hex. P.NAK - Negative Acknowledge - DE hex. Does that look like any protocol anyone has seen before? Jim