Meaning of simple set-up (LOGIC board)

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In summary, the conversation discusses a lab on LOGIC gates where the instructor drew a figure on the board and asked if anyone knew its significance. The figure appears to show incorrect placement of diodes, which could represent ESD protection for the IO line. The conversation also touches on the source of ESD and different methods of protection.
  • #1
sandy.bridge
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Hello all,
I had a lab pertaining to LOGIC gates, and the instructor drew something on the board (without elaborating) and asked us if we knew the significance of what he had drawn on the board. No one knew, and as such we moved on. However, I am now wondering. Attached is what he had drawn. To me it looks rather pointless. Is it supposed to signify a one way path (input----->output), or am I missing something?
 

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  • #2
sandy.bridge said:
Hello all,
I had a lab pertaining to LOGIC gates, and the instructor drew something on the board (without elaborating) and asked us if we knew the significance of what he had drawn on the board. No one knew, and as such we moved on. However, I am now wondering. Attached is what he had drawn. To me it looks rather pointless. Is it supposed to signify a one way path (input----->output), or am I missing something?

It looks like the figure is wrong. If the right-hand diode went to Vcc, then it would represent ESD protection diodes for the IO line.
 
  • #3
Does ESD come from outside of the circuit, or is it from within (or both)? If the cathode of D2 is exposed to a potential of Vcc, then essentially D2 is cut off unless the potential at the I/O exceeds ~(Vcc+0.7V)? The way I am seeing it is if a voltage is applied to D2, then I/O is not grounded.
 
  • #4
ESD generally comes form external sources (like people touching your device). The diodes are both cut off normally, and only conduct when there is a negative (bottom diode conducts) or positive (upper diode conducts) ESD transient that hits the IO line. You either use a bypass cap on Vcc to help get the ESD transient current back to ground through the upper diode, or some folks prefer to use a fast Zener diode to clamp the upper diode to ground, as in the below figure.

http://www.ce-mag.com/archive/03/ARG/Images/03ARGCE82c.jpg
 
  • #5
Interesting. Thanks!
 

1. What is a logic board?

A logic board, also known as a motherboard, is the main circuit board in a computer or electronic device. It contains the central processing unit (CPU), memory, and other essential components that allow the device to function.

2. What is the purpose of a logic board?

The main purpose of a logic board is to provide a central platform for all of the electronic components in a device to communicate with each other and perform their designated tasks. It also serves as the backbone of the device, providing power and connectivity.

3. How does a logic board work?

The logic board works by receiving and sending electrical signals between all of the components in a device. The CPU, which is the brain of the device, processes these signals and carries out the instructions given by the software or user.

4. What is the difference between a logic board and a motherboard?

The terms logic board and motherboard are often used interchangeably, but there is a slight difference. A motherboard is typically used to refer to the main circuit board in a PC, while a logic board is used in other electronic devices such as smartphones, tablets, and game consoles.

5. Can a logic board be repaired or replaced?

Yes, a logic board can be repaired or replaced, but it requires specialized knowledge and equipment. In most cases, it is more cost-effective to replace the entire device rather than just the logic board. However, if the device is under warranty, it is recommended to have a professional repair or replace the logic board.

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