How to distinguish between 7-bit and 8-bit SMS coding formats?

There are three short message codes: 7-bit, 8-bit and UCS2 (16-bit).

7-bit encoding is used to send ordinary ASCII characters. It encodes a string of 7-bit characters (the highest bit is 0) into 8-bit data. Remove the highest bit of each character, and every 8 characters can be "compressed" into 7. 8-bit coding is usually used to send data information; UCS2 encoding is used to send Unicode characters. The maximum capacity of the user information segment of a PDU string is 140 bytes, so the maximum number of characters of the short message that can be sent under these three encoding methods is 160, 140 and 70 respectively.

I don't know if this is clear, don't blame me for digging my own grave ~