Hi All,,

what is the difference between the following connections for MCLR PIN of PIC MCU ?



why we dont connect The MCLR directly to VDD?

what is the purpose of R,R1,C and D ?

Regards

 

This looks and sounds like a homework assignment.

 

This looks and sounds like a homework assignment.

No

 

Hi All,,

what is the difference between the following connections for MCLR PIN of PIC MCU ?


View attachment 139042
why we dont connect The MCLR directly to VDD?

what is the purpose of R,R1,C and D ?

Regards

MCLR=Master Clear pin External Reset.

See here and consult the data sheet for whatever PIC you are using.

In your first diagram, series resistor (R2) is used to prevent over-current damage from ESD voltage spikes. See here (figure 12.2 and related text), for example.

Your second figure does not have MCLR connected to anything. If the pin is configured internally as reset rather than an input pin, it is pulled up, internally to Vdd. If your drawing should show a connection, it is the "older" style of pulling MCLR up.

Your third figure shows the same scheme as your first figure plus a diode, to enhance ESD protection I think. It also shows a capacitor which will lengthen the MCLR pulse if the externally applied pulse is very short.

 

The #3 drawing is for in-circuit serial programming and should include a switch to isolate (disconnect) the capacitor when programming and connect when the circuit is in use in an electrically noisy circuit (especially with inductive loads. The capacitor will insure the device does not reset unintentionally.

The Device will not program if the capacitor is there. Or, it will program if Vpp is connected directly to/MCLR and R1 is at least 10k.

 

Picmicro use the the method shown on all their prototype boards, with the exception of the diode. The ICP Mclr pin is also connected to the MCLR pin.
It is usefull if needing to reset during operation.
Max.

 

The #3 drawing is for in-circuit serial programming and should include a switch to isolate (disconnect) the capacitor when programming and connect when the circuit is in use in an electrically noisy circuit (especially with inductive loads. The capacitor will insure the device does not reset unintentionally.

The Device will not program if the capacitor is there. Or, it will program if Vpp is connected directly to/MCLR and R1 is at least 10k.

The top diagram is from Microchip. Is the diode positioned correctly in the TS's? I initially thought that circuit was from an ICSP application, and maybe I am just looking at it wrong but it did not seem right. Explain please?

 

View attachment 139057

The top diagram is from Microchip. Is the diode positioned correctly in the TS's? I initially thought that circuit was from an ICSP application, and maybe I am just looking at it wrong but it did not seem right. Explain please?

It looks like the Microchip drawing is wrong.
With the diode as it is shown, the resistor/capacitor on the diode's anode will not do anything useful.

 

I believe Vpp is high voltage (12, iirc). The diode is to prevent it from flowing on to the power rail.

 

I believe Vpp is high voltage (12, iirc). The diode is to prevent it from flowing on to the power rail.

That is true but the diode also prevents the reset circuit from driving the MCLR pin low.

 

I have have had no problems using the PMicro boards with the circuit shown in #6, when using ICP.
Max.