When using RS232, the serial connections between the computer and SMINI are made using the 3-pin header along the top right edge of the card. 5.25Vdc. Most surplus computer power supplies easily meet this requirement and are typically available for zero or near zero cost. Besides being more than twenty times faster and much more powerful than the MC68701 used in the original design USIC, the programmed PIC16F877 is about half the cost. These connectors, used on all previous C/MRI board designs, have proven to be extremely rugged, dependable and cost effective. Mod is a universal device that combines the ability to have any protocol support. This is typically handled by the protocol being used on top of RS-485, such as Modbus or Profibus.For example, in a Modbus network, each message sent by the master starts with the address of the device it’s intended for. It is a complete self contained node, being sort of a gee-wiz do-all type of card. For example, the two sets of 24-pin outputs are noted as Cards 0 and 1 located along the left and bottom edge of the card. The 24-pin inputs are noted as Card 2 along the right edge. The left header connects with the cable running back toward the computer and the right header connects with the cable running to the next node.

5Vdc and ground, use the two screw terminals at the top right corner of the card. Although all the I/O lines are physically on the same SMINI card it is convenient to talk about them as being separate (I/O) cards within the same (SMINI) card. Each railroad device being interfaced simply connects directly to one or more of these pins. A CRC or checksum can be added to the end of the data being transmitted. This means that only the U7 transmitter on one particular SMINI can be permitted to be active at a time, otherwise there would be more than one U7 trying to pull the transmission line high or low at the same time resulting in a confused state. VERSITRON is one of the most popular manufacturers of RS-485 standard devices such as 4 channel phone kits with RS485 data transmission capabilities, RS-485 2-wire telephone modems, and so on.

If you prefer, all the circuit boards, including the SMINI, can be purchased fully assembled and tested or as complete kits from SLIQ Electronics. If you have purchased your SMINI already assembled and tested, you may skip to Computer Connections. Converters between RS-485 and RS-232 are available to allow a personal computer to communicate with remote devices. RS-485 discusses that it is used for devices up to 10Mbit/S, then says they need not be limited to 10Mbps. It also states that "the upper bound is beyond the scope of this Standard". You do not need to understand electronics to build the SMINI. The SMINI has six 8-bit output ports labeled as Ports A, B and C for "Cards 0 and 1." Similarly, the three 8-bit input ports are labeled as Port A, B and C for "Card 2." Each I/O port includes an important buffer between the railroad’s connection to the SMINI card and the PIC16F877. With the PIC16F877 everything is handled electronically. Circuit cards and programmed PIC16F877 chips are readily available from JLC Enterprises; all you have to do is follow my instructions. When a "bad message" shows up on the cable, it is more difficult (but not impossible) to figure out which node(s) transmitted that message when you have a shared-medium with a dozen nodes connected to the same single cable, compared to a point-to-point medium with only 2 nodes connected to any particular cable.

If you happen to have one of these early SMINI cards simply ignore the 1, 2 and 3 printing on the card and treat them as if they read 0, 1 and 2. See section Counting Cards/Nodes Using Number Zero in Chapter 2 for change in approach. If more than one segment happens to be turned on, the software within the SMINI defaults to using the baud rate corresponding to the highest switch segment with an "on" setting. Version I is recommended for indoor use, version E is within an IP56 box and can therefore be used in more difficult conditions. Because there can be up to 128 SMINI cards connected on the same 4-wire cable, the system must be able to discern between which SMINI is involved with communications at any point in time. They can easily update one PC, which will take care of all prices to the store.

If you have any issues pertaining to in which and how to use RS485 standard, you can make contact with us at our own site.