Phone Talk / Apple Talk

On Mon, 30 Aug 2004 17:53:08 -0700 Ron Hudson <ron.hudson(a)sbcglobal.net> asked: First some definitions: Appletalk is the protocol that Apple used for connecting to printers and other computers. Localtalk is the hardware specification. Looking around for the latter will give you a lot more information. The problem Apple (and others) solved is how to connect multiple RS232 (RS422) devices together without blowing everything to bits. Their solution was to use a transformer with two independent windings on the primary and one on the secondary (along with a few resistors). The secondary windings are paralleled among the various devices. The primaries are connected to the Tx and Rx of the RS232. This makes for a simple two-wire network. Normally, the ends of the secondary bus are terminated in 110 Ohm resistors. Apple's implementation used proprietary cables. Third party boxes (Farallon, etc.) used RS11 phone cables. I've seen these boxes at various charity outlets in the recent past going for next to nothing. If you have an old phone modem laying around (parts - not collectable...) you can use the output coupling transformer to make an adaptor. They generally have the two-primary/one-secondary format and have the correct ratio. The receiver side of the primary should be terminated with a couple hundred Ohm resistor. As a side note, there are a lot of Localtalk printers and the like showing up for cheap. Connection to Windoze and Linux boxes are generally a problem. There are cards that talk Appletalk, but they are fairly scarce. However, there are a number of bridges coming available that connect ethernet to Localtalk and the Appletalk drivers are available for both OSs. CRC