![]() ![]() This is extremely useful in situations such as handling chip select or output enable pins of external ICs where those pins only need to drive to the source voltage or ground. With a decoder those same three pins (the two address pins and the digital output pin) could be instead used to interface with eight peripheral components thanks to the power of binary arithmetic (2 3 = 8). If there is no need for a controllable output signal then it might be more desirable to instead use a decoder. The third pin serves as a digital output whose signal then can be redirected to up to four external peripheral components by toggling the address pins into one of four states including = 00, 01, 10, and 11. With a demultiplexer we can take two of the microcontroller’s I/O pins and turn them into address pins (for example A1 and A0). Figure 1C: A multiplexer takes inputs from multiple devices, selected using the microcontrollers address pins, and routes the desired components output to a single input pin on the microcontroller. Figure 1B: A decoder takes address pins as inputs and raises the corresponding pin to a logic high. Figure 1A: Demultiplexer can route a data output pin to different components based on address pins. Circuits such as multiplexers, demultiplexers, and decoders come in a variety of packages and voltage levels so they can be incorporated into a board layout with relative ease. Another possibility is to incorporate an additional circuit that sits between the microcontroller and the various external components. Depending on component availability or design constraints this might not be a possible option. Of course, one option would be to explore larger chips within the same microcontroller family. After accounting for power, ground, reset, and the I 2C pins on a small 8-pin chip like an ATtiny85, a design might at most interface with three external peripherals using the remaining I/O pins. Fewer peripherals means less functionality which tends not to be a desirable tradeoff.Įven when utilizing bus-based protocols such as I 2C or SPI, there is often a need for each external integrated circuit to have a pin dedicated for chip select or output enable (often notated as CS or OE on schematics, or /CS and /OE for active low variations). Physically smaller packages have less room for I/O pins meaning fewer peripheral components can interface with the microcontroller itself. These benefits do come with a cost, however. Logisim that did not provide an enable input.The relentless march of technological progress has given engineers increasingly smaller and more energy efficient microcontrollers to use in their designs. The attribute is primarily for supporting circuits built using older versions of ![]() Include Enable? The component has an enable input when this attribute is yes. In the latter case, the output is effectively disconnected from any other ports. Disabled Output Specifies what each bit of the output should be when the component isĭisabled (i.e., when the enable pin is 0). Data Bits The bit width of the data being routed through the multiplexer. The number of inputs to the multiplexer will beĢ selectBits. Select Bits The bit width of the component's select input on its south edge. Select Location The location of the select and enable lines relative to the component. ![]() Facing The direction of the component (its output relative to its input). The digits '1' through '4' alter its Select Bits attribute,Īlt-0 through Alt-9 alter its Data Bits attribute,Īnd the arrow keys alter its Facing attribute. When the component is selected or being added, Regardless of the data and select inputs. South edge, right side (input, bit width 1) Enable: When 0, the multiplexer's output consists of all floating bits, On the west edge to route to the output on the east edge. South edge, left side indicated by gray circle (input, bit width matches Select Bits attribute) Select input: The value of this input determines which input If the select input contains any unspecified (i.e., floating) bits, East edge (output, bit width matches Data Bits attribute) The output value will match the input values on the westĮdge whose number is the same as the value currently received Spelling.) Pins (assuming component faces east, select is bottom/left) West edge, variable number (inputs, bit width matches Data Bits attribute) Data values, one of which is to be routed to the output.Įach input data value is numbered, starting with 0 on the north. (Incidentally, some authorities spell this I find it useful to think of a multiplexer as analogous to a railroad The east edge which of the inputs to copy is specified via theĬurrent value received through the input on the south edge. Copies an input on the west edge onto the output on ![]()
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