По мне, так стандарт - этоPin No. Name Dir Notes/Description1 - - Protective/shielded ground2 TD OUT Transmit Data (a.k.a TxD, Tx) (ASYNC)3 RD IN Receive Data (a.k.a RxD, Rx) (ASYNC)4 RTS OUT Request To Send (ASYNC)5 CTS IN Clear To Send (ASYNC)6 DSR IN Data Set Ready (ASYNC)7 SGND - Signal Ground8 CD IN Carrier Detect (a.k.a DCD).9 - - Reserved for data set testing.10 - - Reserved for data set testing.11 - - Unassigned12 SDCD IN Secondary Carrier Detect. Only needed if second channel being used.13 SCTS IN Secondary Clear to send. Only needed if second channel being used.14 STD OUT Secondary Transmit Data. Only needed if second channel being used.15 DB OUT Transmit Clock (a.k.a TCLK, TxCLK). Synchronous use only.16 SRD IN Secondary Receive Data. Only needed if second channel being used.17 DD IN Receive Clock (a.k.a. RCLK). Synchronous use only.18 LL - Local Loopback19 SRTS OUT Secondary Request to Send. Only needed if second channel being used.20 DTR OUT Data Terminal Ready. (ASYNC)21 RL/SQ - Signal Quality Detector/Remote loopback22 RI IN Ring Indicator. DCE (Modem) raises when incoming call detected used for auto answer applications.23 CH/CI OUT Signal Rate selector.24 DA - Auxiliary Clock (a.k.a. ACLK). Secondary Channel only.25 - - Unassigned