However the actual value calculated my change depending on the logic family because the leakage current will vary.
You can see that the equation works for regardless of the TTL or CMOS Glue Logic Family used TheĬapacitance is the trace and the addition of all the devices on the The Resistor calculation: R = (t / 0.4 x C T). The formula for the required pull-up resistor value is: So with in 0.8uS the input will float to 0.8v Voltage/Time = I OZ / C = 20uA / 20pF = 1v/uS
Leakage current on the line and the load capacitance The not to exceed float time is calculated from the The value is chosen to pull the line high before the gateįloats to 0.8v. To large a resistor value will slow the rise time of the gate voltageĬausing the voltage to linger in the transition region leading to output To calculate a pull-up resistor value so that the receiving gate is pulled highīefore the input rises into the transition region of the gate. Off, leaving the receiving gate floating. V IH V cc -Īnother equation is used for the case when all the Tri-State devices are Because only one Three-State output should beĪctive at any given time the calculation for the pull-up resistor is the Devices with Three-State outputs may beĬonnected in parallel.
Additional names for Tri-State include High-Impedance State, or Off-State. Valid logic level so the output remains fixed at a valid voltage level Tri-State Output pins should be tied to a While in the off-state the IC will neither sink current or source current, the outputs just represent a high impedance condition. When the IC is placed in the 3rd state, neither transistor is conducting and is said to be in the off-state. Normally an ICs output is either high or low, depending on which of the output transistors is on and conducting. Normally the two transistors that make up the output circuit of a transistor will function in opposition, one is conducting while the other is not. Output enable lines are control lines that allow the Totem Pole Outputs to function as normal, or shut them both off depending on the state on the control line.
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