On Mon, 22 May 2017, Paul Koning via cctalk wrote:
Does your PC have real RS232? A lot of "RS232" ports are serial ports, but not with correct RS232 levels. If you have "TTL RS232" [sic] it won't work with an actual RS232 port.
The "CLASSIC" example: manager of the Radio Shack Computer Center told me that the TRS80 Model 1 Expansion Interface RS-232 board was, "by definition" completely "standard" for RS-232, since "RS-232" stood for "RADIO SHACK 232".