GE GFK-0804B 用户手册

A message is sent as a series of characters.  Each byte in a message is transmitted as a
character.  The illustration below shows the character format.  A character consists of a
start bit (0), eight data bits, an optional parity bit, and one stop bit (1).  Between charac-
ters the line is held in the 1 state.

Stop

Start

MSB                     Data Bits                            LSB

  Parity 
(optional)

 

10                9               8        7         6        5        4        3        2        1        0

Each station monitors the time between characters.  When a period of three character
times elapses without the reception of a character, the end of a message is assumed.  The
reception of the next character is assumed to be the beginning of a new message.

The end of a frame occurs when the first of the following two events occurs:

H The number of characters received for the frame is equal to the calculated length of

the frame.

H A length of 3 character times elapses without the reception of a character.

Timeouts are used on the serial link for error detection, error recovery, and to prevent
missing the end of messages and message sequences.

After sending a query message, the master should wait approximately 500 milliseconds
before assuming that the slave did not respond to its request.