From comp.dcom.lans Thu Mar 18 19:59:10 1993 Xref: ipmce comp.sys.ibm.pc.hardware:2388 comp.dcom.lans:14 Newsgroups: comp.sys.ibm.pc.hardware,comp.dcom.lans Path: ipmce!zaitcev From: zaitcev@ipmce.su (Pete A. Zaitcev) Subject: Re: Cheepest way to connect two IBMPC's (RS-232) ???? Message-ID: Organization: Inst. of Prec. Mech. & Comp. Equip., Moscow, Russia References: <1993Mar11.073446.3479@ericsson.se> <1993Mar12.172931.27983@hippo.ru.ac.za> Date: Wed, 17 Mar 1993 14:58:03 GMT Dear collegues! In <1993Mar12.172931.27983@hippo.ru.ac.za> ccml@hippo.ru.ac.za (Mike Lawrie) writes: >For information, my PC connected via about 1.5 miles of cable to our >mainframe from RS232 plug using only the Tx and Rx pins (ie pins 2 and >3) via our telco's 2-wire cabling. This worked at 1200 bd without error >for several years. Now I use 4-wire simply-built RS422 drivers at 19,200 >bd, error free. In the Moscow State University such achievements are often, especically on the Dept. of Physics. But you should be warned: this is play with a fire. Approximately half of year ago when I worked in the Scientific Research Computing Center of the MSU there was a hard storm. The flash hit the building and burned two ports on PCs, which were connected by the UTP (~150 meters in distance). Other RS-232C devices are suffer from interference also. CRT serial interfaces on the Phys. Dept. are also burnt when the electron accelerator in the ground flour shot (not every time, but often). I suggest to decide to use the COM-to-COM connection only when: 1) your computers consume the power from the one substation or have a massive common ground; 2) the cable is shielded, the shield doesn't carry the signal ground (pin 7 on the DB-25), the shield is conneced on the one side. 3) there is no other possibility (mini-modems, current loop, etc). For now, the CL-to-RS232 converter. In Moscow it costs less than 1489/1488 which you have to repair after the storm. Hope it will be useful on the West, too. CL 20mA +---+ D1 4+---+ D2 3+---+6 D3 <---+---!SW ! +--!& ! +-------!F O-----> _!_ ! ! ! ! !6 ! 1! ! RS232 /_\ ! O----* ! O----+ +-----! ! ! ! ! ! 5! ! ! 2! !7 <---+---! ! +--! ! ! ---! O-- VD1 +---+ +---+ ! +---+ 9!& ! ! ! +--! !8 ! ! ! O------+ !10! ! +--! ! ! +---+ ! --- +5V A or +12V ! !\ ! VD2 ! <--! >!---+ +----------> !/ ! ! +-+ ! ! R1 +---+ ! ! 4.7KOhm +--! !---> +-+ ! +---+ RS232 ! 12+---+ D2 / 250 Ohm *------*-------*--!& ! / ! ! ! ! !11 #/ VT1 +-+ R2 ! VD3 ! ! O-----# | | _!_ !13! ! #\ 2.2KOhm| ! /_\ +--! ! \! +-+ ! +---+ -J ! ! ! ! ! ! --- --- --- D2 is the 74LS00, I guess. Other components surely have western substitution, but I don't know a names. The D1 optrone is of phototransistor type, 10mA opening current. The D3 is the in- tegral TTL-to-line driver with two power supplies. SY, Pete