Tham khảo tài liệu 'electronic navigation systems 3e episode 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Serial data communication 409 Figure Typical arrangement for the transmission of an ASCII character using the RS-232 standard. Voltage levels could be in the range 5 to 15 V for the loaded driver stage. If a voltage level of 10 V is assumed and with the data transmitted as an 8-bit group consisting of 7 data bits and a parity bit the arrangement would be as shown in Figure . The 8-bit group is framed by a start bit at logic 0 and a stop bit at logic 1. If the group represents an ASCII character then the use of 7 bits can only allow AScIi values up to 127. The RS-232 standard supports two types of connectors a 25-pin D-type connector DB-25 and a 9-pin D-type connector DB-9 . The pin assignments for a DB-25 connector is shown in Table Table DB-25 pin assignment Pin Signal Source Key 1 - - Frame ground 2 TD DTE Transmitted data 3 RD DCE Received data 4 RTS DTE Request to send 5 CTS DCE Clear to send 6 DSR DCE Data set ready 7 SG - Signal ground 8 DCD DCE Data carrier signal 9 - - Positive voltage 10 - - Negative voltage 11 - - Unassigned 12 SDCD DCE Secondary DCD 13 SCTS DCE Secondary CTS 14 STD DTE Secondary TD 15 TC DCE Transmit clock 16 SRD DCE Secondary RD 17 RC DCE Receive clock 18 - - Unassigned 19 SRTS DTE Secondary RTS 20 DTR DTE Data terminal ready 21 SQ DCE Signal quality detector 22 RI DCE Ring indicator 23 DRS DTE DCE Data rate selector 24 SCTE DTE Clock transmit external 25 - - Busy 410 Electronic Navigation Systems Table DB-9 pin assignment Pin Signal Key 1 DCD Data carrier detect 2 RD Received data 3 TD Transmitted data 4 DTR Data terminal ready 5 SG Signal ground 6 DSR Data set ready 7 RTS Request to send 8 CTS Clear to send 9 RI Ring indicator Typically in many applications only nine of the DB-25 pins are important and the DB-9 connector reflects this as shown in Table . Considering the DB-25 connector signals are carried as single voltages referred to a common earth point SG pin 7 . The TD pin 2 connection allows data to .
