shermaine said:
Hi there,
I got a few questions before i start wiring your layout to test out.
Q(1) Does dip switch need 1kohm resistor ?
Do i need 3 1kohm resistor or 2 1kohm resistor?
Q(2) What does max/min 15 refers to?
Q(3) Why does input of U3a and U3b needs to connect to clk?
Q(4) Why 2 input of U3C need to connect to 5v?
Q(5) For Qb bar of U6b, do we need to conenct to gn?
Q(6) For dip switch, why does it need to conenct resistor to 5v?
Q(7) For IC 74191, why does A,B,C,D & En need to conenct to gnd?
Q(8)These unconected QA & QB, do we need to conenct to any point?
Q(9) What does D/U refers to pin?
Please advise soon.Thanks.
A(1) TTL does not need pull up resistors since Open = High. But CMOS does.
So you can insert resistors if you wish. You only need 2 since D1 does not do anything.
A(2) Look at the data sheet for the 74191. Max/Min is high at 15 if the counter is counting up or high at 0 if counting down.
A(3) Because your tutor asked that the LEDs flash. This makes them flash at the clock rate.
A(4) Because it is used as an inverter. Again, you can leave them open if you wish since it is a TTL IC.
A(5) No. Qb bar of U6b is an output and MUST be left open.
A(6) I answered this in A(1)
A(7) If you look at the data sheet, you will see that En is Active Low. So if you want the counter to count, this pin must be connected to gnd.
The A, B, C & D inputs must be connected to gnd so that 0000 will be loaded when the Load pin is set low. This is necessary since the IC does not have a reset pin.
A(8) No. Unused outputs MUST be left open.
A(9) Read the data sheet. This is the up/down control. Low = Up.
Don't forget to connect 100 nF bypass capacitors across the Vcc and gnd pins of the ICs. You may experience strange results if there is insufficient bypassing.
Attached is an alternative gating arrangement that yopu may wish to consider. I've also attached my gating paper for your info.