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Now let’s talk about keypad, keypad is nothing but multiplexed keys. See also Robotic Vacuum Cleaner Using Atmel Mega32
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In the circuit you can see that we have used 8bit communication (D0-D7) however this is not a compulsory, we can use 4bit communication (D4-D7) but with 4 bit communication program becomes a bit complex. So from mere observation of above table we are connecting 10 pins of LCD to controller in which 8 pins are data pins and 2 pins for control. PIN5 or RW (Read/Write) to ground (puts LCD in read mode eases the communication for user) PIN4 or RS (Register Selection) to PD6 of uC PIN3 or VEE to ground (gives maximum contrast best for a beginner) The connections which are done for LCD are given below: We just need to control ENABLE and RS pins to send characters and data accordingly. This puts LCD in highest contrast and read mode. In the circuit, you can observe that I have only took two control pins, this give the flexibility, the contrast bit and READ/WRITE are not often used so they can be shorted to ground.
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