PIC 16C57C MCU CIRCUIT DESIGN QUESTION

[yce_kelvin]

Hi, i am new on pic mcu design. i am get a tutorial from school and i do not understand the circuit theory... some one can help me?? or if u got any information about this mcu design then can share with me?? thanks.

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anyone can give any suggestion answer on the file i attach??

 

[motion]

On the first schematic, the transistor serves to increase the amount of current output from the PIC's port pin to be able to drive the relay. The circuit is known as an "emitter follower" or buffer.

On the second schematic, the PNP transistor turns ON when the voltage exceeds a preset value determined by the zener breakdown voltage plus about 0.5V (the voltage across the base and emitter terminals of the transistor). A PIC16C57 might not startup correctly with a slowly rising power supply even with its built-in delay. This circuit ensures that the PIC remains reset until the power supply voltage reaches the minimum required for it to operate.

 

[yce_kelvin]

oh, ic.. thank you.. thanks your help.

 

[StupidDum]

Reset circuitry is required in microcontroller like 8051.
However, I think PIC doesnt require this, right?
I usually just tie it to Vcc with 10K resistor.

 

[yce_kelvin]

ya..this we just connect to the vcc by resistor.. but this one is little different... that's y i ask urs.. becoz this circuit diagram is from a company..and the lecture take out some of the part for us to research...so, i just need some understanding on the circuit design.

 

[Nigel Goodwin]

ya..this we just connect to the vcc by resistor.. but this one is little different... that's y i ask urs.. becoz this circuit diagram is from a company..and the lecture take out some of the part for us to research...so, i just need some understanding on the circuit design.

The external circuitry on the MCLR pin is for improved "brown out" detection. The 16C57 is an extremely old PIC (10+ years?), modern ones have better internal "brown out" detection - but on the old ones, if you had a dodgy power supply, you could add it externally.

BTW, if you want any 16C57's, I have about 200 or so sat in tubes!.

 

[yce_kelvin]

sorry.. i still got a question on the circuit... what is the function of the component diode, zener diode and transistor 2n4002 and 1n4007 in this circuit??