The hardware design does not use pin processing, it is divided into these three steps!

With the increasing scale of integrated circuits, today's large-scale chips have integrated many functional modules, but in the actual circuit design, we can not use all the functional modules (or interfaces) of the chip. There will always be more or less pins that "will not be used". How do these unused pins generally be handled?

For unprocessed pins, the author is divided into three steps:

The first step: pin classification

Many people begin to have headaches as soon as they hear the classification. There are so many types of pins and the level of the interface is not the same. How do you classify them?

In fact, the classification here is based on a simple basis, that is, whether the pin is input or output?

Oh, it seems that there is a type of Bidirectional that is both an output and an input. Generally, this type of pin is usually viewed as an output pin.

For the output pin, unless the chip has special instructions and requirements, it can be directly suspended.

Step 2: Compare the manual

The general chip manual will have more detailed descriptions and requirements for the use of pins. The following is a description of three input pin processing in Altera's FPGA manual:

The fourth column clearly states that for the two pins DEV_CLRn and DEV_OE, they need to be directly grounded when they are not used, and can be left unconnected if the DATA[5:15] signal is not used. .

After the second step, most of the input pins have the proper processing. Then the question is, there will always be some input pins. Even if the manufacturers have searched every corner of the manual, the manufacturer has not given a reasonable disposal proposal. What should we do?

The third step: handle the pin function

As mentioned in the second step above, for some unused input pins that the manufacturer does not give advice on disposal, you can do some basic processing actions according to the function of the pins: Some pins of the clock input function are not used. In this case, it is better to be grounded directly or grounded through a pull-down resistor to prevent the pins from being disturbed and affecting the normal operation of the chip. Some enable control pins, if not used, are best pulled down to a fixed function trigger level, allowing the pin to have a stable reference level input.

Pins for hardware configuration functions need to be fixed at a high level or a low level when not in use. Of course, most chips generally have a default pull-up match, and you can also select dangling, but if If it is a more sensitive signal, an external pull-down will be much more reliable.

The last great move, for the very few pins in the uncertain case, it is best to set aside the pull-down resistors, debugging can be based on the actual performance to choose whether to pull up or pull down.