# What does 'DC' in DC-20 Mhz operating frequency of a microcontroller means?

#### viznu3391

Joined Dec 10, 2015
16
Can anyone please tell what does DC in oscillator specification of a microcontroller means ?

#### Alec_t

Joined Sep 17, 2013
12,060
Direct Current, i.e. 0Hz.

#### viznu3391

Joined Dec 10, 2015
16
Direct Current, i.e. 0Hz.
This is where I get confused. since oscillator is running in 20MHz frequency, then what does this 0Hz implies?

#### jpanhalt

Joined Jan 18, 2008
11,088
"0 Hz" means that the MCU is specified down to DC for its clock. Now, a DC "clock" might not be useful, but you might want to use an external clock at a much lower frequency than, say 32 kHz. Maybe for some applications something as slow as 10 to 100 Hz might have a use. You can also clock through a program at a very slow pace.

John

#### viznu3391

Joined Dec 10, 2015
16
"0 Hz" means that the MCU is specified down to DC for its clock. Now, a DC "clock" might not be useful, but you might want to use an external clock at a much lower frequency than, say 32 kHz. Maybe for some applications something as slow as 10 to 100 Hz might have a use. You can also clock through a program at a very slow pace.

John

Thanks for the quick reply.I didn't think in the way that it is actually specifying the range of frequencies it can operate.

Thanks all

#### hp1729

Joined Nov 23, 2015
2,304
Can anyone please tell what does DC in oscillator specification of a microcontroller means ?
It implies that the clock signal can be stopped without loosing operations. Older processors had a minimum clock frequency. I have never tried it but you might be able to step a processor through operations at a manual clock speed if it says that it goes own to DC.

#### Papabravo

Joined Feb 24, 2006
16,072
It also means you can stop the clock in either the high state or the low state for an indefinite period of time and then continue without losing any information. It requires that the internal circuitry be constructed with static memory. The opposite of static memory is dynamic memory which requires periodic refresh cycles or the bits just sort of disappear.

#### alfacliff

Joined Dec 13, 2013
2,458
most of the processors are dynamic logic, they have to have a clock running. if the clock stops, the processor usually wither quits, or fails. the RCA 1802 is one of the early processors that actually was made with static logic, you could clock it with a switch, and it still worked if the clock stopped look up "static and dynamic logic".