CD74HCT40105: MASTER RESET (MR) Pulse Timing.

Hello Yuyama-san,

Hiroaki Yuyama TED said:

In the data sheet of "CD74HCT40105", the Master Reset signal states that it is reset by inputting a pulse signal.
Please tell me the details of the pulse signal.

The MR input is level controlled, but requires a minimum pulse width to properly operate.

You can see the exact logic functionality here:

In the "Prerequisites for Switching" section of the datasheet, the minimum pulse width for the MR input is defined:

Hiroaki Yuyama TED said:

・Low time from power ON to rise of MR signal

This is not a specification of the device.

I would recommend providing at least the maximum propagation delay time provided in the datasheet before beginning operation, as the device may have unknown internal states at startup and this is the minimum time to ensure all states have stabilized.

For 2-V operation, this would be 3750 ns.

Hiroaki Yuyama TED said:

・If the power ON and MR signal rise timings are the same, will the reset be enabled only by the fall of the MR signal?
*In the specifications, the time for the High section of the reset pulse is described, but I couldn't find it for Low.

No, the MR input is level triggered, it is not edge triggered or pulse-width triggered. As long as the MR pin is held HIGH while the supply is within the recommended operating voltage range and the minimum pulse width is provided, then the device's memory will be cleared. Note my answer above in regards to allowing the device to stabilize prior to starting operation.

Hello Yuyama-san,

Yes, my recommendation can be given to the customer. Please note that this is a public forum - all of my advice is available to all customers from here, and I will not post something that I do not recommend to tell to the customer.