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Interfacing one4x4 keypad with two 8051 microcontrollers at a time

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kalyaniupen

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My project is Interfacing one 4x4 keypad with two 89 c55wd ics. That means the keypad connected to one 89c55wd should display the same data on both LCDs. C code is same for two controllers.Please suggest me.Already hardwired same keypad to two microcontrollers but not working.LCDs are not displaying same data.
 

Doesn't work without special coding. The controllers need to synchronise their scanning action, or one control is actively scanning and the other only reading the lines.
 

Hi,

I agree with FvM.
But the "slave" needs to read both lines and rows.

If it is for redundancy (safety) reasons:
* both should work exactly identical.
* during start up they should "read" and check for activity
* in case there is activity, they stay in slave mode
* in case there is no activity, the should start "master" mode by driving the rows actively.

In case one stops master mode, the other will detect this and takes over master mode.

*****
In case redundancy is not needed, then it's far easier that one performs the scanning and transmits the results to the other microcontroller via UART.

Klaus
 

Hi,

I agree with FvM.
But the "slave" needs to read both lines and rows.

If it is for redundancy (safety) reasons:
* both should work exactly identical.
* during start up they should "read" and check for activity
* in case there is activity, they stay in slave mode
* in case there is no activity, the should start "master" mode by driving the rows actively.

In case one stops master mode, the other will detect this and takes over master mode.

*****
In case redundancy is not needed, then it's far easier that one performs the scanning and transmits the results to the other microcontroller via UART.

Klaus

This is for redundancy only
 

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