Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise . 74ls,, 74ls Matched Datasheet Manufacture, PDF . 1, 74ls, BIT SHIFT REGISTERS, Texas Instruments, 74ls pdf. Texas Instruments 74LS Logic – Shift Registers parts available at DigiKey. SN74LSDW Datasheet · SN74LSDW – Texas Instruments ·
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This is an area where a microcontroller excels – scanning a keyboard matrix in your case 4×4. There are also purpose built chips that scan the buttons connected as an array like the 74C That will mean you only need three pins on the micro and a suitable algorithm to manipulate the datashdet register.
I’m assuming the inputs are already pulled high by some means. Pressing SW1 pulls down IN0 only. You can use a couple of 74LS encoders as shown in their data sheet. Available output returns to a low level when the entered key is released – even if another is depressed.
P1 through P15 are inputs for parallel-loading the shift register. If the voltage is negative, then reverse the direction of the diodes. I’ve searched the forums and it doesn’t look like anyone has asked this yet.
But it’s better to show them here for completeness, remember next person searching the web and finding this question may have a different micro or idea in his head. Pressing SW4 pulls down IN2.
74LS673 (Big) 16-bit serial-in serial-out shift register
Has anyone 74ld673 this particular shift register before? Add pullup resistors if necessary. Pull-ups are required, may be internal to micro or not. Yes, I finally have a reason to use the “diagonal diode” symbol in CircuitLab. If you use more than one of these ICs together with their outputs tied to the same input, you’ll need to manage the CS pins in order to ensure that both ICs don’t try to deliver data at the same time.
The logic diagram on the bottom of page 4 shows why: There are other ways that use many diodes. Though having 16 buttons using that method would be pushing that technique a tad. Do I gather that you also want to be able to somehow recognize N-key press events? With all of these you would need to handle debounce in code.
As in the picture: A simple solution is to connect a diode from each input to every switch that should pull that input low. That looks like Trevor’s “Visio-Lab”. You need to modify your question to clarify that you want to prevent eatasheet button pressed simultaneously giving an erroneous code.
I’ve just acquired two 74LSs and need help understanding the datasheet.
74ls datasheet & applicatoin notes – Datasheet Archive
He just wants to “send a ground” to the input signals. Home Questions Tags Users Unanswered. Email Required, but never shown.
Such an arrangement is called a “diode matrix”. To change any data in the shift register at all, the clock must have a falling edge.
clock, data and latch on the 74LS
Since it’s only 15 switches, another way this can be done is to use a shift register rather than an array. Pressing SW2 pulls down IN1 only. You forgot the pull-ups though. Feed one output low through the shift register and read back the status on the common line. I have to do this without one button influencing the other.
That’s what diodes are for. Yes, my inputs are already pull-up, the problem is that with this type of configuration I can only recognize one key at a time, if I activate keys 1 and 2 at the same time the input will receive 3. Sign up or log in Sign up using Google.
(PDF) 74LS673 Datasheet download
There are also purpose built chips that scan the buttons connected as an array like the 74C Or if you have the ability to program one, a small ROM or FPGA can do it. A simple diode arrangement datwsheet encode the buttons. Another alternative is to turn your buttons into a rudimentary digital to analog convertor and feed that analog value into whatever analog to digital convertor you may have available.