Since stop bits are always 1 (mark bits), the two modes are equivalent. Instead of sending a parity bit and a stop bit, two stop bits are transmitted. The mode 8M1 (8 data bits, MARK parity, 1 stop bit) can be emulated with 8N2. This is relatively simple to implement and cannot be distinguished by the receiver. The modes 7M1 (7 data bits, MARK parity, 1 stop bit) and 7S1 (7 data bits, SPACE parity, 1 stop bit) can easily be emulated using 8N1 (8 data bits, NO parity, 1 stop bit) and setting the 8th data bit to 1 resp. How can MARK and SPACE parity be used on these systems? Solutions (Note that PARMRK has nothing to do with MARK parity.) The manpage of of the Unix/Linux termios library, for instance, doesn't say a single word about these two parity modes. MARK and SPACE parity, although implemented in most hardware, are not defined in the POSIX standard. Therefore, these modes are sometimes referred to as CS9 (9 data bits). MARK and SPACE parity does not allow detecting transmission errors, but it may be used as an additional information bit. With SPACE parity, the parity bit is always 0. With MARK parity, the parity bit is always 1 (independent of the data bits). the first stop bit immediately follows the data bits.īeyond these three modes, there are two other modes: MARK and SPACE parity. With NO parity, the parity bit is not sent at all, i.e. With ODD parity, the parity bit is set to 0 if there is an odd number of 1's in the data bits. With EVEN parity, the parity bit is set to 0 if there is an even number of 1's in the data bits. This bit is transmitted between the data bits and the stop bit(s). EVEN or ODD parity allows the receiver to detect (not correct) single-bit errors at the expense of sending one additional bit per byte. Most serial port transmissions use EVEN, ODD or NO parity. Since there is very few information available on this topic, I summarize here what I know about it. When developing the libmip library, I faced the problem of MARK/SPACE parity under Linux.

Bit parity