INTRC:INTOSC :using internal clock

[lipschutz]

HI

i am using 16f88 on a project. i want to configure the internal oscillator at 4MHz. now that i have two unused pins: pin 15 and 16. i am gonna ground this pins through a 3.3k resistor. but is that okay? i read somewhere that one of this pin is used to control the system clock frequency. so i need clarification on that point. please advise or refer me any doc that would be helpful.

thanks in advance.

 

[misterT]

please advise or refer me any doc that would be helpful.

The datasheet: https://www.electro-tech-online.com/custompdfs/2013/04/30487c.pdf

From the Pin Diagram at page 1 you can see that the pins 15 and 16 can be used as oscillator input (OSC1 and OSC2). From the page 35 onward you can get more info about oscillator configurations etc.

 

[jpanhalt]

Why do you want to ground the pins?

John

 

[lipschutz]

this pins will not be used anyway. but as you know unused pins are the source of all sort of problems. my point is whether it is okay to ground the pins through a resistor? or if i do so will it cause to change circuit performance some other way? let us see what is the source of confusion: here is the reference--

Article:1.4.4.4 , page:28/29
PIC MICROCONTROLLER know it all
publisher: newnes
ISBN: 978-0-7506-8615-0

Some PIC microcontrollers (e.g., PIC12C672 and PIC16F628) have built-in oscillator circuits
and they do not require any external timing components. The built-in oscillator is usually setto operate at 4 MHz and is selected during the programming of the device. For example, the
PIC16F62X series of PIC microcontrollers can be operated with an internal resistor–capacitorbased
4-MHz oscillator (called mode INTRC). Additionally, a single resistor can be connected
to pin RA7 of the microcontroller to create a variable oscillator frequency (called ER mode).
For example, in the PIC16F62X microcontroller OSC1 and OSC2 pins are shared with the
RA7 and RA6 pins, respectively. The internal oscillator frequency can be set by connecting
a resistor to pin RA7 as shown in Fig. 1.22. Depending on the value of this resistance, the
oscillator frequency can be selected from 200 kHz to 10.4 MHz (see Table 1.8). When used in
this mode, pin RA7 is not available as a digital I/O pin.

 

[jpanhalt]

this pins will not be used anyway. but as you know unused pins are the source of all sort of problems. my point is whether it is okay to ground the pins through a resistor? or if i do so will it cause to change circuit performance some other way? let us see what is the source of confusion: here is the reference--

The need to ground CMOS inputs applies mostly to logic chips. For the 16F88, just set the pins as outputs.

John

 

[lipschutz]

those pins are already set as outputs.

thanks
lipschutz

 

[jpanhalt]

They do not need to be grounded when set as outputs (low-impedance). The general reference manual for the mid-range chips does give one example where grounding may help reduce system noise, and that is when an external oscillator is used on the other pin. That is not what you are doing, however.

Here's an image of that section (page 40):



John

 

[lipschutz]

thanks John, i will certainly take a note of that.

lipschutz