16F877 upgrade to 18F4620

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- 4th January 2008, 19:58
earltyso

16F877 upgrade to 18F4620

I am finally jumping up to the 18F big boy toys....
I just ordered my first 18F4620 to replace a 16f877A I am using in an LCD board with lots of I/O's, 4x20 LCD, TX/RX and such. I have never used this chipset before. Can anyone tell me what to expect for possible programing problems, compatibility issues, and also how to use the internal oscillator of can I use my XT???

I am looking forward to the 4X Kword upgrade which is why I chose this chipset.

I would really appreciate any help.
- 4th January 2008, 20:11
skimask

Quote:

Originally Posted by earltyso

I am finally jumping up to the 18F big boy toys....
I just ordered my first 18F4620 to replace a 16f877A I am using in an LCD board with lots of I/O's, 4x20 LCD, TX/RX and such. I have never used this chipset before. Can anyone tell me what to expect for possible programing problems, compatibility issues, and also how to use the internal oscillator of can I use my XT???

I am looking forward to the 4X Kword upgrade which is why I chose this chipset.

I would really appreciate any help.

Should be a piece of cake to do... In my mp3 player project, I went from a 16F877 to a 18F452 to a 18F4620 without changing any hardware, just rewrote the firmware a bit when changing chips.
Just pay attention to the datasheets. Register names vary between PIC families.
If you've got something going, and it isn't going, chances are you haven't read the datasheet far enough.
- 4th January 2008, 22:16
earltyso

thanks

thanks for the help,
Have you used the internal oscillator on this chipset? up to 40Mhz according to the datasheet.
- 4th January 2008, 23:23
mister_e

more likely up to 32Mhz. Internal osc can go up to 8 MHZ, then you multiply it X4 (PLL)...

40MHz is when you're using an external 10MHz crystal + PLL enabled.
- 5th January 2008, 07:30
skimask

Quote:

Originally Posted by earltyso

thanks for the help,
Have you used the internal oscillator on this chipset? up to 40Mhz according to the datasheet.

The datasheets says it'll run UP TO 40Mhz internally, by using the 4xPLL, meaning the most you can put in externally is 10Mhz.
I've had ONE run at 25Mhz on an external clock (by mistake before I read the datasheet closely), but that's not the norm and most likely won't work for others, not to mention it ran a bit flakey, locked up often, that sort of thing.

EDIT: Ya, what Mr.E said...I really should read first...
- 5th January 2008, 15:42
earltyso

thanks again

Thanks again for the help!
- 5th January 2008, 17:00
Jumper

Are we reading the same datasheet?

I downloaded the pdf file from microchip's webpage and read it.

It said:

Two External Clock modes, up to 40 MHz

These 2 modes are:

9. EC External Clock with FOSC/4 Output
10. ECIO External Clock with I/O on RA6

So it is not possible to use the PLL in these modes but the PIC will run at 40 Mhz if it has a 40 Mhz oscillator connected. I run several 4620 on 40 Mhz, both as 10 Mhz +4*PLL and as pure 40 Mhz circuits.

Also can this be found under absolute maximium ratings:

All devices 15 35 mA -40°C
VDD = 4.2V
FOSC = 40 MHZ
(PRI_RUN,
EC oscillator) <--------- look here!!!
16 35 mA +25°C
16 35 mA +85°C
All devices 21 40 mA -40°C
21 40 mA +25°C VDD = 5.0V
21 40 mA +85°C

So there should be no problem at att to run a 18F4620 with EC or ECIO configuration bits from an external 40 MHz oscillator if Vdd > 4.2V and if it is an industrial rated PIC (figure 26-1) the LF and extended rated PIC has a different behaviour.

/me
- 6th January 2008, 06:28
skimask

Quote:

Originally Posted by Jumper

I downloaded the pdf file from microchip's webpage and read it.
It said:
Two External Clock modes, up to 40 MHz
These 2 modes are:
9. EC External Clock with FOSC/4 Output
10. ECIO External Clock with I/O on RA6
/me

I'll be.... guess I should have read further into it.
Oh well. Run 10Mhz external gives the option of a sort of clock throttling anyways, switching between the various oscillators, both internal and external. I use it a lot to save battery juice.