Question ---- Single Chip Microcomputer matrix keyboard row and column inversion scanning method, single chip microcomputer Matrix

Question ---- Single Chip Microcomputer matrix keyboard row and column inversion scanning method, single chip microcomputer Matrix

I learned some questions about the C code written by others on the Internet using the matrix keyboard. I hope I can see some help.

 

Schematic diagram of matrix and independent keyboards:

Principle:For the matrix keyboard on the right of the figure, set the four lower bits of the P3 port (P3.0 ~ P3.3) and 4-bit (P3.4 ~ P3.7) Set 1 separately. If a key is pressed, a certain position of the corresponding P3 port will be pulled down from the high level, the row and column values are measured respectively to determine which button is pressed.

For example:First, assign the four low bits to the high level, that is, P3 = 1__1111. If S15 is pressed, P3.2 is pulled to the low level, that is, P3 = 1__1011, in this case, the four-digit high level is P3 = 1111_0000, so P3.5 is pulled into a low level, that is, P3 = 11000000000. Finally, add the two tested P3 values 1__1011 + 11000000000 = 11000001011 (the row and column values are the third row and the second column)

(1) The most common online statement:

1 P3 = 0x0f; // 0000 1111 2 if (P3 & 0x0f )! = 0x0f) // key detection 3 {4 delay (3); // software shake 5 if (P3 & 0x0f )! = 0x0f) // key detection 6 {7 row_value = P3 & 0x0f; // scan row value 8 P3 = row_value | 0xf0; 9 colume_value = P3 & 0xf0; // scan the column value 10 // while (P3 & 0xf0 )! = 0xf0); // float detection 11 return (row_value + colume_value); 12} 13}

(2 ):

P3 = 0x0f; // 0000 1111if (P3 & 0x0f )! = 0x0f) // key detection {delay (3); // if (P3 & 0x0f) of the software shake )! = 0x0f) // click the button to check {row_value = P3 & 0x0f; // scan the row value P3 = 0xf0; colume_value = P3 & 0xf0; // scan the column value // while (P3 & 0xf0 )! = 0xf0); // returns (row_value + colume_value );}}

 

(3 ):

P3 = 0x0f; // 0000 1111if (P3 & 0x0f )! = 0x0f) // key detection {delay (3); // if (P3 & 0x0f) of the software shake )! = 0x0f) // key detection {row_value = P3; // scan row value P3 = 0xf0; colume_value = P3; // scan column value // while (P3 & 0xf0 )! = 0xf0); // returns (row_value + colume_value );}}

 

(4) This is in line with the Principles and Examples I mentioned:

P3 = 0x0f; // 0000 1111if (P3! = 0x0f) // key detection {delay (3); // if (P3! = 0x0f) // key detection {value = P3; // scan row value P3 = 0xf0; value | = P3; // scan column value // while (P3! = 0xf0); // returns (value );}}

I have used the Development Board for actual testing. The above four are all correct.

My questions:I don't understand why you need to write common statements.& 0x0f, & 0xf0Or| 0xf0What is the special role of this writing? I feel that both writing and not writing are correct. Why should I write? (Especially when writing 1 and 4 seem quite different) ------------------ 22:05:02

 

 

 

 

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