jtt@cunixd.cc.columbia.edu (James T. Tanis) (11/27/90)
I'm trying to get my ms-dos and apple machines talking. Apparently, what I need is a 'null-modem' cable. Could some kind soul tell me what this is? i.e - what the pin connections are supposed to be. Thanks! -JT
johnston@oscar.ccm.udel.edu (11/27/90)
In article <1990Nov26.191130.10237@cunixf.cc.columbia.edu>, jtt@cunixd.cc.columbia.edu (James T. Tanis) writes... >I'm trying to get my ms-dos and apple machines talking. Apparently, what I >need is a 'null-modem' cable. Could some kind soul tell me what this is? >i.e - what the pin connections are supposed to be. The following cable recipes assume that one is connecting a Mac Plus or later. For more information, see Tech Notes 10 and 65 which give the pin definitions for the RS-422 protocol. Mac (mini-8) PC (DB-25) ------------ ---------- 1 <--------------> 6 3 <--------------> 3 4 <--------------> 7 5 <--------------> 2 This is a 'MacLink Plus' cable. We copied this one -- it works. (I don't think that the 1 <----> 6 connection is needed for most applications.) Mac (mini-8) PC (DB-25) ------------ ---------- 3 <--------------> 3 4 <--------------> 7 5 <--------------> 2 6, 8, 20 jumpered together This is a Mac to IBM-XT or Compaq Portable cable. Source: SoftPC manual -- Believe it or not, this will work, too. For PC-AT users: Mac (mini-8) PC-AT (DB-9) ------------ ------------ 3 <--------------> 2 4 <--------------> 5 5 <--------------> 3 1, 4, 6 jumpered together Note that the common ingredient to the 3 cable recipes above is that the Mac uses pins 3, 4, and 5 (the middle three on the connector). These correspond to TXD-, ground, and RXD- in the RS-422 specifications -- TD, ground, and RD in RS-232c terminology. Hope I got this right! For what it's worth, on my own home-made cables I use only the transmit, receive, and ground. I tried disconnecting the handshake lines and neither computer seemed to care. It's always possible that some application requires them, but I haven't found one yet. Also, I strongly recommend buying rather than making the null modem cable, unless you LOVE soldering to tiny mini-8 connectors with thermoplastic housings that soften when heated. It should be possible to buy a MacLink Plus cable. MacLink Plus is a product of Dataviz, Inc. 203-268-0030. Here is one cable vendor (quoted from a posting by another net person) which supplies raw materials: Micro Computer Cable Co., in Romulus, Michigan, sells mini-din connectors,cables, switch boxes, crimp tools, cable, etc., at resonable prices. Their phone numbers are 313-941-6574 FAX, 313-941-6500 I haven't used this vendor personally, but the quote was from a satisfied net.customer. Happy cabling! Misco (800)876-4726 and Black Box (412)746-5530 also supply raw materials. Bill (johnston@oscar.ccm.udel.edu) Bill Johnston; 38 Chambers St.; Newark, DE 19711; (302)368-1949