Astream.Write expects an array of bytes (a byte array)
So, if you already have such an array (like buffered_byte), this should work:
async.Write(buffered_byte)
In the above code, you pass the whole array to async.write.
Otherwise, to pass individual byte values, you must pass them as an array, like Erel suggested:
async.Write(Array As Byte(0xFE)) ' one value
async.Write(Array As Byte(0xAB, 8)) ' two values
async.Write(Array As Byte(3,buffered_byte(5),7)) 'three values
Obviously, as you already know, trying to pass single byte values, will NOT work:
async.Write(7)
async.Write(buffered_byte(5))