maximum crystal frequency

[Munib]

I have been using 8051 mcu with crystal of 12MHz.Now i am going to use PIC18F452.The maximum crystal frequency given in datasheet is 40MHz

My question is what is the effect of using higher operating frequency i mean if there are some special considerations while writing code or it is just as normal.

is there any special external circuitry considerations for using higher operating frequency?
I have to interface this mcu with a RF module with center frequency 418MHz.

Also when using 8051 it is more convenient to use 11.059MHz rather than 12 MHz
because with 11.059MHz it is easier to find an integer value to be loaded in TH1 for generation of baudrate.It is very convenient without disturbing the operating speed much.

Is there such case for PIC18F452? If yes then please specify that crystal frequency.

I personally think that as most of the instructions of PIC take 4 clock cycles thus if i will choose Crystal whose frequency is some multiple of 4 then timing calculations will be straight forward.


And if some one has used PIC18F452 tell me the part number for the crystal used

 

[Kuller]

operating frequency of 8051 with crystal of 12mhz

I have been using 8051 mcu with crystal of 12MHz.Now i am going to use PIC18F452.The maximum crystal frequency given in datasheet is 40MHz

I am using PIC 18f458 for a little proyect with a 20 mhz crystal without any external "special" circuit.

If you see the datasheet You only can reach 40 mhz by using a 10 mhz crystal and activating the 4x internal PLL

My question is what is the effect of using higher operating frequency i mean if there are some special considerations while writing code or it is just as normal.
is there any special external circuitry considerations for using higher operating frequency?
I have to interface this mcu with a RF module with center frequency 418MHz.

The only external circuits you need for 20 mhz (i didnt work at more speed) are 2 C's & XT, you can find the right values for your crystal on the datasheet. Usually 15nf is fine.

And about the tranceiver... You will have to look for the interface it needs (Dont think the center frequency cares)

Also when using 8051 it is more convenient to use 11.059MHz rather than 12 MHz
because with 11.059MHz it is easier to find an integer value to be loaded in TH1 for generation of baudrate.It is very convenient without disturbing the operating speed much.

Is there such case for PIC18F452? If yes then please specify that crystal frequency.

Well, perhaps for your application you can use another frequency i cannot help you on this :/

I personally think that as most of the instructions of PIC take 4 clock cycles thus if i will choose Crystal whose frequency is some multiple of 4 then timing calculations will be straight forward.

All the intructions of PIC take 4 clock cycles to complete.

And if some one has used PIC18F452 tell me the part number for the crystal used

 

[ilker]

why crstal frequency in 8051 is 11.059mhz

do you know any standart crystal frequencies over 11.0592 Mhz for an integer boudrate on at89xx ?

 

[IanP]

For 8051 and AT families there is next crystal of 22,1184MHz.
It is just 2 x 11,0592..

 

[checkmate]

I've used PIC18s running on 10MHz crystals with PLL enabled to clock at 10MIPs. Serial comms is not a problem here.