TTL and CMOS gates help?

Question

how can i solve this question i have no idea how to start :((

Design a logic interface circuit to allow the connection of data from either of the two specific
logic gates shown (one TTL and one CMOS), to either of two other specific logic gates (TTL
and CMOS)

the gates are
CMOS 4001M to TTL 74LS00
TTL 7402 to 74HC00

Specifications
1. Five volt power supplies are used on both source and destination circuits.
2. The signal must not be inverted in passing through the interface. (It may of course be
inverted within the interface, but must emerge the same as it went in).
3. The interface is to contain an LED (with current between 5mA and 10mA) to indicate the
state of the data (at point X), as well as any extra gates (of any type) needed to provide the
interface function. (Use gates only, not transistors).
4. The interface must be properly designed to ensure that it takes into account the worst case
specifications of the logic gates involved. D.C. design only is required.

Answer 1

Start by geeting the data sheets for those devices. I never heard of a 4001M, usually they come in B and UB varieties, but it shouldn't make any difference.



For each pair of gates and for each of the two logic states you have to decide whether the output voltage of gate 1 lies within the acceptable input voltage range for that particular logic state for gate 2, under all possible conditions of input current.



Example: 4001 & 74LS00 & logic 0



Maximum input voltage at input of 74LS00 that will be recognised as a logic 0 = 0.8V



Maximum possible current required to drive the LS00 to logic 0: from the internal diagram of the LS00 the input looks like a 20k resistor in series with a shottky diode. So, at Vin = 0.8V, input current will be ( 5 - (0.8 + 0.3) ) / 20,000 = 0.195mA. Allowing some variation in resistor value, let's call it 0.22mA.



Maximum possible voltage on 4001 output when sinking this current: From the 4000 series data book, a gate can sink at least 0.8 mA when its output is 0.8V.



Conclusion: at logic 0 a 4001 can drive a LS00 without any problem.



Now repeat for the other 3 permutations.



This is what I think you will find:



4001 to LS00: Works perfectly.

7402 to 74HC00: Works at logic 0, output voltage too low at logic 1. Solution: Put a pull-up resistor from output to +5V.



Then all you need is another gate with a LED on its output to indicate the state of the line. Use a HC gate because it has a high input impedance so won't drive the line, and it has enough output current to drive a LED.

Answer 2

you have 4 different logic families to interconnect. Look at the input and output specs for each one and see if they can be connected together and still meet all of the specs. I think they can with perhaps the addition of a pull up resistor.



You have 2 different connection paths as you list.



for example,

TTL 7402 has a VOH of >2.4 volts at a source current of 400µA and a

VOL of <0.4 volts at a sink current of 16 mA



74HC00 CMOS has an input high (VCC=4.5v) of >3.15v at 20µA

and input low of <1.35 volts at 20µA



Those numbers work, except for the 20µA. A TTL gate in the low state can sink current, but it cannot source current. A pullup resistor of (4.5–3)/20µ = 75k (use 68k) will fix that.



You should be able to do the rest. Use a separate CMOS gate to drive the LED.



.

Answer 3

Maybe you could use something like an 74-ls-244 buffer driver device here. Check the max current to see if you could drive a modest LED by configuring two of these devices in parallel, using one to pass data and the other to drive the status LEDs. See partial data sheet below.

Answer 4

Cmos 4001

Answer 5

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