VK5OI wrote:You are correct of course, it is old fashioned. That is why I wonder why (some) big name new radios are only equipped with TTL level comms. You can of course buy a USB to radio "programming lead" or build one, which is what most hams do.
I am trying to avoid either removing the radio from the car, taking a laptop to the car, or running a long cable to the car every time I want to reprogram the radio's memory channels.
Most, if not all, devices use some form of shifting internally by using a RS232 IC (eg. the above mentioned MAX232). Just bypassing this chip allows you to connect the ESP directly to the TTL/CMOS logic of the device, no need to do this shifting yourself. This is probably not the case for real legacy devices, but for your radio it should work this way.