confusion in using latch register and port register

[himanshu mittal]

Sir,
I am new to pic microcontroller and trying to learn from friends.
I am doing led blink program on pic 16f877a.
I am confused whether to use port register or latch register.
When i used latch register in blinking led
LATB=~LATB
Delay();

complier shows error like undefined LATB
When i used port registr led start blinking
PORTA=~PORTA
Delay();

Engineergarage is using latch register in their tutorial but some are using port register in led blinking.
I am totally confused whether to use latch or port register.

I am also unable to understand what is Read modify write operation.

[AJISH ALFRED]

Hi,

Avoid using statements like this in your ‘C’ code.

LATB=~LATB 

PORTA=~PORTA 

 

Take a temperory variable, say ‘t’ and convert the above statements like,

 

t = LATB;

LATB = ~t;

 

t = PORTA;

PORTA = ~t;

 

Port registers are connected to the port pin through Latch registers,

 

PORT REGISTER >> LATCH REGISTER >> PORT PIN

 

Even if you write a value to the port register, it will not appear at the port pin until you enable the latching using the lacth registers. 

For a simple LED blinking, writing a ‘1’ or ‘0’ to port register (according to whether the anode or cathode of LED is connected to the pin) and then keep on enabling and disabling the latching will do the purpose.

[himanshu mittal]

Thank u

[Author]

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