ZIP-LAN.TXT 8.0 MULTI-PC APRS ZIP-LAN networks! The ZIP-LAN concept is a trivial way to connect a classroom full of PC's together to a single TNC so that students can all play with the MIREX experiment. In MIRMON, the MASTER mode is disabled so that only the main PC connected to the TNC can transmit via the TNC but all can listen and send messages back and forth between each other. Here is an edited version of the normal APRS ZIP-LAN.TXT file... ZIP-LAN is a way of connecting many co-located APRS PC's together in the field so that they can all communicate with each other and a single TNC for powerful multi-PC APRS support of an event or emergency. A ZIP-LAN is just a single wire and ground, as in ZIP-cord. Everyone listens for APRS data on the wire, and sends their RS-232 data to the wire. Only one TNC is needed and it puts everything it hears on the wire. Therefore all PC's hear everything locally and from the TNC. ALso they can all transmit to each other and the MASTER. For MIRMON, only the MASTER can transmit via the TNC. Each ZIP-LAN PC can have its own call and can communicate fully among each other! This is perfect for MIRMON in a classroom. The hardware concept is simple, Everyone sends and receives everything to the single ZIP-LAN wire. The diodes and 15 K reisitors provide the "ORing" function so that anyone can drive the ZIP-LAN wire. *--/\/\/--* : +--------+ | | : | PC |3--------*--->|----* | One wire LAN | LOCAL | | | | #1 |2<-----------------*------* +--------+ | | *--/\/\/--* | +--------+ | | | | PC |3--------*--->|----* | (ground not shown) | LOCAL | | | | #2 |2<-----------------*------* +--------+ | +-------+ | | | *--------------------- | ----------------->* TXD | | | | | | | | | +--------+ | | | TNC | | PC |3--* | *--/\/\/--* | | | MASTER | | | | | | | |2<------------------------*----*---|<----*---<* RXD | +--------+ | | | : +-------+ : Notice that the diode and 15K resistor easily fit in the DB-9 shell. The recommended zip connector is nothing but two wire pigtails with insulated aligator clips on the end. You connect to the ZIP cord with ordinary PINS pushed through the insulation. At the MASTER you put the diode and resistor between a back-to-back connector with the two pigtails hanging so it can be inserted between any existing TNC and its PC. (come as you are) DIGIPEATER OPERATIONS: Notice that the MASTER does not send to the ZIP- LAN but only to the TNC. This means that there must be a digipeater on the air for the MASTER's packets to get digipeated back to the LAN.... For MIRMON, this is an excellent confirmation that the MASTER's packets got to MIR and back. Until MIR comes into view, if you want the MASTER to be able to send packets to the ZIP-LAN, there must be a temporary digi in place, or switch to the APRS freqency in your area. OPERATIONS: Simply bring up all of the local PC's in ZIP-LAN mode, and the master station operates normally. Local PC's both send and receive on the ZIP-LAN, but only the Master sends to the TNC. Master packets get to the local PC's by being digipeated on the air... Resistor values may need to be increased or decreased depending on your particular serial port requirements. I typically 10k for the TNC and 15k or so for the others. This should work over several hundreds of feet and up to 5 PC's or more. Or MAYBE LESS. I have used DIODE-ORing of RS-232 successfully for 19 years with good results. BAUDRATE! Operating at 9600 baud will minimize collisions if there will be more than a few PC's generating traffic. Collisions will garble packets half as much at 9600 as the 4800 default. But long wire runs at 9600 baud may also suffer errors in a noisy environment, so experiment and see what is best for your application. ALL PC's and the TNC must be at the same rate. You may consider adding 300pF Caps in each interface to ground to bypass any RF that might get on the wire. COLLISIONS: Since the local PC's share the single ZIP-LAN wire for both send and receive, there may be some collisions when the local PC's transmit. For this reason, where practical, the MASTER should be used to generate the bulk of the outgoing traffic. Also, since there can only be one POSIT ICON at the whole LAN location, the ZIP-LAN PC's will not originate any POSITS, except for the Master. Similarly, enter NONE for their STATUS beacons, unless needed. Theoretically, with a max'ed out 1200 baud APRS channel (36% busy), and operating the ZIP-LAN at 9600 baud, the LAN is only busy less than 4% of the time so colisions should be minimal. TNC INTERFACE: The master is connected to the TNC in the normal fashion, so it can handshake with the TNC as needed for configuration and changing the UNPROTO path. The other PC's can't touch it.