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Here we will see how Chip can be used to interface a matrix keyboard with microprocessors. But generally, it is used as keyboard interfacing. In this mode, the matrix keyboard can have only four rows.
There are eight columns. These can be selected using RL these eight column lines. At the intersection of each row and column, there is a key. There are another two keys. These keys are Shift key and the Ctrl key, these two keys are not the part of the matrix. The key structure looks like this -. In the decoded mode the scans the keys by making logic 0 for each row at a time, and then each of the eight columns is read.
Let us see an example of this keyboard scanning mechanism. Let us consider that currently, it is scanning row 3 by sending the select line values , and the received information is from RL It is indicating that the RL 6 is at logic 0.
The LS 3 bits indicating the column numbers Here means the column 6 and next 3 bits are indicating the row number Here for row 3.
As there are four rows in the keyboard so 2-bits are sufficient, but there are three bits One additional bit for row selection. When the ctrl and shift buttons are not pressed, then these two fields will hold 1.
After scanning the keyboard key, the IRQ is activated by If another key is pressed in that time, that information is added after the previous key information in FIFO RAM like a queue structure. The structure of this register is like below. It starts from and incremented by 1. When the interrupts of the processor are disabled, and the user is pressing seven keys, then the value of the last three bits will be So if another key is pressed, the F flag will be set to 1, and three bits will become It will generate an Over-run error.
It will set the O flag. This O flag indicates the Over-run error. Similarly, when the F flag is 0, and the last three bits are also , then it indicates that the FIFO RAM is not full and also it has no character to read.
In the decoded mode there are only four rows. In most of the cases, the is used in Encoded mode of operation. In this mode, we can set eight rows and eight columns to connect 64 keys. Like the decoded mode, it also has shift and control key. So by adding these two with 64, there are 66 keys. From this diagram, we can see that one external decoder is used. The SL3 is not used. The decoder output is connected with the eight rows of the matrix. The following table is showing the pattern shown by theSL by for scanning keyboard.
Let us consider that currently, it is scanning row 5 by sending the select line values , and the received information is from RL The LS 3 bits are indicating the column numbers Here means the column 6 and next3 bits are indicating the row number Here for row 5. Interfacing Keyboard with Microprocessor Microcontroller Microprocessor Chandu yadav. Previous Page Print Page. Next Page.
Interfacing 8279 Keyboard with 8085 Microprocessor
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The Intel is used for keyboard interfacing but it can also be used for multiplexed 7-segment LED display interfacing. To display a character into 7-segment display we have to store 7-segment code in a display RAM location. The display RAM of this chip can store 16 bytes of data. To write to the display RAM one special command is needed to be applied on the control port. The following pattern is showing the RAM command that is written to the control port of
Here we will see how Chip can be used to interface a matrix keyboard with microprocessors. But generally, it is used as keyboard interfacing. In this mode, the matrix keyboard can have only four rows. There are eight columns. These can be selected using RL these eight column lines.