Comments on Mutually exclusive enable for TMUX1108 (8:1) and TMUX1104 (4:1) using SN74LVC1G240 — safe POR and logic review
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Mutually exclusive enable for TMUX1108 (8:1) and TMUX1104 (4:1) using SN74LVC1G240 — safe POR and logic review
I have two analog multiplexers on the same net (WORK_ELEC):
For 4:1 MUX Enabled is going through an Inverter .
They must be mutually exclusive (never enabled at the same time). Additionally, I want both MUXes disabled at power‑on (POR).
Control Signal:
A single digital control: WE_MUX_EN (from AD5941). Desired behavior:
WE_MUX_EN = High → Enable 8:1, Disable 4:1
WE_MUX_EN = Low → Disable 8:1, Enable 4:1
At POR (before firmware drives WE_MUX_EN): both disabled.
My schematic is given below. May I know my logic is correct or not.
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Hello, happy new year.
Nice Shematic. To be honest, it should not work as posted. The reason being, according to the SN74LVC1G240 datasheet, when both pins 1 (NOT_OE), and 2 (A) are low, the output (Y) is High. This would enable the 4:1 MUX at every Power-On.
Instead, you could use two D-Type FlipFlops as a binary counter; Connect the FlipFlops as a binary counter (picture bellow); Connect both FlipFlop's CLK inputs to WE_MUX_EN from the AD5941; Connect each MUX_EN to a different FlipFlop Q output.
At power on, if WE_MUX_EN is low, both FlipFlop's outputs are off. When the firmware pulls WE_MUX_EN High, the first MUX turns ON; On the next WE_MUX_EN High, the first MUX turns OFF, and the second turns ON; To alternate MUXes, simply pulse WE_MUX_EN High.
Dual D-Type FlipFlop as binary counter
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