1. Is official RS-232 (EIA-232) standard open and free available? I couldn't find it in Internet.
2. Does "RS-232 with TTL levels" is covered by some standard?
3. Does "synchronous RS-232" (via USART) is covered by some standard?
4. Is there general name for RS-232-like protocols with different voltage levels?
Best Answer
(disclaimer: this is from memory, it was 15y ago that I had to study these standards.)
Contrary to what most people seem to think the RS-232 and similar standards describe only the electrical aspects, and at a very crude level the function of the handshake lines. The data format is NOT described in these standards.
=== 1 Is official RS-232 (EIA-232) standard open and free available?
No, it is not free. (Note that there are three: RS, TIA/EIA, and CCITT/ITA.)
=== 2 Does "RS-232 with TTL levels" is covered by some standard?
No. That would leave only the data format aspect, which was not in the standards in the first place.
=== 3 Does "synchronous RS-232" (via USART) is covered by some standard?
I assume you mean data transfer accompanied by a synchronous clock? I don't recall, because that was not what I was after when I read the standards. I vaguely recall that there is provision for a clock line, but not even a mentioning of the clock level on which the new bit should be shifted out.
=== 4 Is there general name for RS-232-like protocols with different voltage levels?
I assume you mean the asynchronous serial data format? The fancy name for that is non-return-zero start-stop. non-retrun-zero (NRZ) means simply that a 0 is tranmitted as one level and a 1 as another level, without any extra edges inserted or removed (as for instance Machester or NRZI would do). start-stop means that a start bit (polarity oppisite to the idle polarity) is prepended, and a stop bit (polarity same as idle polarity) is appended.
I always found it strange that a 'standard' that is used so widely is not standardised. But when I tried to find the standard description of SPI I found the same situation.