I'm doing some circuit design employing an ARM MCU and I've run across a stumbling block.
Most MCUs claim to implement one or more "USARTs", but what's meant today isn't what has been traditionally meant--and it lies in the area of what "synchronous" means in terms of traditional communications protocol.
Traditionally, synchronous serial communication has meant that the data stream is sent with a clock (can be recovered or synthesized) with no gaps between characters. In other words, it's a block-oriented protocol--there are no start bits or stop bits--just one long stream of data bits. To accomplish this, a special character (usually ASCII SYN) is sent as a preamble to the block and is used as filler within the block should data not be immediately available. To make this work, the receiving USRT employs "hunt mode", which is essentially a search on the incoming data stream for one or more SYN characters. The search is done on a "sliding window" basis, such that every time a new bit is clocked in, a comparison is made. When this results in a match, the character framing for successive data bytes is established.
Apparently, someone early on decided that for MCU communication, all "synchronous" meant was that an external clock would be employed--the data sent would still have start bits and inter-character spacing--sort of async with external clock.
In the past, I've used real USARTs, such as the 8251 or 2661 in my application, but they're rapidly fading into history. So my question is this: Is there any MCU out there with "hunt" capability on serial communication?
Most MCUs claim to implement one or more "USARTs", but what's meant today isn't what has been traditionally meant--and it lies in the area of what "synchronous" means in terms of traditional communications protocol.
Traditionally, synchronous serial communication has meant that the data stream is sent with a clock (can be recovered or synthesized) with no gaps between characters. In other words, it's a block-oriented protocol--there are no start bits or stop bits--just one long stream of data bits. To accomplish this, a special character (usually ASCII SYN) is sent as a preamble to the block and is used as filler within the block should data not be immediately available. To make this work, the receiving USRT employs "hunt mode", which is essentially a search on the incoming data stream for one or more SYN characters. The search is done on a "sliding window" basis, such that every time a new bit is clocked in, a comparison is made. When this results in a match, the character framing for successive data bytes is established.
Apparently, someone early on decided that for MCU communication, all "synchronous" meant was that an external clock would be employed--the data sent would still have start bits and inter-character spacing--sort of async with external clock.
In the past, I've used real USARTs, such as the 8251 or 2661 in my application, but they're rapidly fading into history. So my question is this: Is there any MCU out there with "hunt" capability on serial communication?