Signals

Signals represent the passing of information between various symbols. Signals may be of type:

• Digital

  Digital signals are the most common signals, hence a typical program can be comprised of between 95% and 100% digital signals. This type of signals can have only two states, often referred to as on/off. Other common descriptors are high/low, active/inactive, or 1/0. Usually actions in a program are triggered by a digital signal going from the low to the high state. This transition is called the rising edge, or positive edge. Although most actions are edge-triggered, others can be level-triggered (based upon current state, not just last transition). For example, a Toggle symbol is edge-triggered; it drives its digital output high and low with each rising edge of its input. In contrast, the Buffer symbol is level-triggered; its ’enable’ digital input signal must remain high for signals to flow.

  As a general rule, digital signals should have only one driving source. But there are two important and common exceptions: system inputs (such as button presses), and the outputs of Buffer symbols. These exceptions can be very useful in applications where functionality must be shared across several user interfaces. For example, a DVD player can be controlled by a touchpanel as well as by a remote control transmitter.

• Analog

  Analog signals are represented by 16-bit numbers, and thus can have values between 0 and 65535. Unlike digital signals, analog signals can vary continuously in value, in the same manner as a parameter such as volume or temperature. Analog signals are often used for controlling devices that do not have discrete on/off settings. Typical applications for analog signals are volume, lighting, and temperature levels, as well as advanced string manipulation.

  Unlike digital signals, analog signals may have multiple driving sources. Thus analog signals are said to be jammable. In practice, whenever more than one symbol is driving the same analog signal, the symbol that lasts changes the signal's value takes precedence.

• Serial

  Serial signals facilitate the transmission of serial data (i.e. strings of characters). These signals can be generated by incoming data on a COM port or by a symbol that has a serial output. Similar to analog signals, serial signals are jammable; thus multiple symbols can be used to generate strings on a single signal. By default, serial signals are transient, meaning that the data on a serial signal is only valid for the logic wave in which it was created. Symbols such as the Make String Permanent symbol allow serial strings to be retained in memory.

Signal names are case insensitive, have a maximum length of 32 characters, must begin with an alphabetic character and may not contain spaces and other characters in this set (“;:”).

Three signal names are reserved: 0, 1, and Local. The two constants represent digital 0 and 1 or analog 0, and will be sent to the symbol when the program starts.

You may also name a signal “//”, or select Complete Argument from the right click menu. The symbol’s argument will be defaulted to either a 0 or to a temporary hidden signal name, which will behave properly as if you don’t care what that argument is assigned to. For more information on this topic please refer to Special Signal Name //.

Note that incomplete signals are marked by an exclamation point icon denoting that the signal is missing either a driving source, or a destination.