MC74ACT273N, Octal D Flip-Flop

[Souper man]

I ordered a grab bag of quality semiconductors, and included was three MC74ACT273N. I found the data sheet and it says it is a Octal D Flip-Flop. D flip flop is data flip flop, but it then says it is Edge Triggered. It does not say how to use it, and I would like to learn how to utilitize it for future Logic projects. any help on how to use?

 

[kjennejohn]

That's a pretty poor data sheet that doesn't tell you how to use it. Try this:

The AC273 and ACT273 have eight edge-triggered D-type
flip-flops with individual D-type inputs and Q outputs. The
common buffered Clock (CP) and Master Reset (MR) input
load and reset (clear) all flip-flops simultaneously.
The register is fully edge-triggered. The state of each Dtype
input, one setup time before the LOW-to-HIGH clock
transition, is transferred to the corresponding flip-flop’s Q
output.
All outputs will be forced LOW independently of Clock or
Data inputs by a LOW voltage level on the MR input. The
device is useful for applications where the true output only
is required and the Clock and Master Reset are common to
all storage elements.

The gist of it is:
There logic levels at the eight D inputs get sent to, and latched at, the Q outputs when the CP pin (the clock input, might be named differently on your sheet) rises from low to high. When the MR (or RST or RESET) pin goes low it forces all the Q outputs low at the same time, regardless of what the clock is doing.
So, in most situations, at the start, the MR pin is made low so all the outputs start at a known level. The clock is either constant high or low. Things remain this way until the clock switches from a low to a high. This is a "rising" edge. This edge makes the output latch the levels at the inputs. These input signals need to be stable a certain amount of (very short) time before and during this latching action. These are called the "setup times", which are given in the data sheet.

These things get used all over the place.
You can drive the inputs on a 7-segment LED display by latching 8 bits of data out of a processor. Using another '273, you can take the same 8 bit port on the same processor and drive another 7-segment display without interfering with the first display. You simply dedicate a few other pins to drive the clock inputs to each individual Flip-Flop. You could use six (more or less) displays by supplying each with its own '273 and six pins to clock and latch the data one '273 at a time.

Hope that helped.
kenjj

BTW, the ACT in 74ACT mean:
A for advanced (faster, less power used)
C for CMOS construction, so uses less power by design
T for TTL levels, so considers a LOW level to be less than 0.8V, while a HIGH is greater than 2V (typically)

 

[Papabravo]

Ahhh....aren't all D flip-flops edge triggered? If its level triggered then it is called a transparent latch, or just a latch for short. JK flip-flops are also edge triggered, sometimes positive edge and sometimes negative edge.

 

[Souper man]

Thank you so much! You get 5 stars!

What is the setup called when you drive a 7segment display with a 273? It came with 3 of them, and I got a 3 digit display, So I would Like to use that. Otherwise, What is that setup called?

Papabravo: I also have 2 negative edge triggered JK flip flops, Isnt that the falling edge of a clock signal or negative power?

 

[ArtemisGoldfish]

Negative edge = falling edge of the clock cycle.

 

[kjennejohn]

Forgot to mention:
The '273 lacks the power to drive the LEDs in the display adequately. You'll have to install something between the '273 and the LEDs. This something can be a ULN2803 driver IC, transistors, FETs... whatever.

The coincidence part: a lot of processors now have adequate drive to power LEDs directly. Still, they have only so many pins, and a latching IC of some kind comes in handy. Of course, you could multiplex the displays to get the job done, but not all jobs lend themselves to this process.

End two cents.
kenjj

 

[Papabravo]

An ACT output should be good for sourcing or sinking 24 mA! Las time I looked that was more than sufficient to drive an LED. The configuration is called direct drive since there is nothing in the 273 that will display a digit.

Also I don't know where your concept of negative power came from. No such thing AFAIK.

 

[kjennejohn]

Wow! I have lived long enough to see a 74-series IC with sufficient drive to light an LED. I'm still operating in the -LS- days when a couple of mils was all you get.

Later!
kenjj

 

[Souper man]

I was thinking of negative power regulators, aka 7900 series of V-regs.

Know any easy circuit involving a 273?

Also, I Noticed that the 273 does not have aQ Output, But has a reset feature instead. What would the Q be though?

 

[kjennejohn]

The inverted Q is the output whose logic level is the opposite of the Q output. You might have a D input whose output is used to enable two different circuits. But, these circuits may use opposite levels for the same purpose. So, some flops and latches provide both a Q and Q-not (inverting) output. In the case of the '273, if you have this situation, you will have to provide an inverter gate or transistor to flip the original level.

kenjj

 

[Papabravo]

Wow! I have lived long enough to see a 74-series IC with sufficient drive to light an LED. I'm still operating in the -LS- days when a couple of mils was all you get.

Later!
kenjj

C'mon a plain old 7438 could light LEDs with no problem at all.
Wahchoo talkin' bout - Willis?

 

[Souper man]

lol, know any websites with some D flip flop projects? Im itching to get started