The SECSI system uses an RS-485 serial line to connect the control computer to multiple control nodes located around the layout. The control nodes can be stand-alone SECSI Daughter II or SECSI CabDriver II single-board control nodes, or SECSI Mother system motherboards, each of which supports up to eight SECSI Daughter II or SECSI CabDriver II as plug-in cards. Stand-alone single-board control nodes can be mixed with motherboard control nodes in the system to simplify wiring, using motherboards in high-density I/O locations such as a CTC panel while using single-board control nodes scattered around the layout.
SECSI Daughter II digital input/output cards provide 16 digital inputs and 32 digital outputs for connection to detectors, signals, turnout motors, switches, lamps and LEDs. SECSI CabDriver II high-current relay cards provide 16 digital inputs and 7 high-current relays to support computer block control or automated block forwarding for block-oriented layouts.
In addition to the simple on/off functionality of the digital outputs on many other systems, the SECSI Daughter II offers operating modes that enhance modeling realism and simplify central computer programming. Flashing signal indications, flashing crossbuck lights, pulse outputs, and support for two-lead LED searchlight signals - including yellow and flashing yellow indications - are supported directly by the firmware. No action by the central control computer is required to continue flashing, crossbuck, or pulse operation once turned on. In addition, no external signal drivers are required to drive two-lead LED searchlight signals, which require an oscillating drive signal to display yellow signal indications.
The SECSI Connector converts the control computer's existing RS-232 interface to an RS-485 serial line to connect the control computer to the SECSI Mothers. While the RS-232 serial line format is limited to connecting two devices 100' apart, the RS-485 serial line of the SECSI system is capable of connecting to dozens of SECSI Mothers up to 4000' from the control computer. The highly noise-immune RS-485 serial line is also much more suited to use in electrically noisy environments, such as the typical model railroad.
Each SECSI Daughter II or SECSI CabDriver II card has an on-board microprocessor with internal UART that converts inbound serial data into parallel output bits and parallel input bits back into outbound serial data. Each card also has a dipswitch address that enables the on-board microprocessor to know which data on the serial line is intended for that card. This approach does away completely with separate serial interface cards and processor cards, and results in a simpler, more compact, and less expensive automation solution.
The system runs on +12 volt filtered DC power, relieving the need for regulated power supplies, multiple voltages, and bipolar supplies, and further simplifying system wiring. Each SECSI Mother motherboard and stand-alone SECSI Daughter II and SECSI CabDriver II card must be provided with but seven wired connections -- power supply +12 volts and power ground, and five RS-485 wires: RCV+, RCV-, XMT+, XMT-, and signal ground. These connections and the additional connections for digital inputs and outputs, throttle leads and block feeders, are all made using Molex connectors, providing easy maintenance and component substitution.