Transitioning from M to H

RP Henry · Joined: 23 Sep 2004 Posts: 1

I have been a happy user of M-level PIC C for years. A new assignment requires me to transition to H level.

Any advice? Warnings? Run away?
_________________
Richard Henry

Guest · Posted: Thu Sep 23, 2004 11:07 am

Have the same question.

I started last week with an 18F252 sample. And did not like this micro at all.
Have been working with 16F88, wich is great for me. The only problem is with memory.
What I would like to find, is a similar chip in 18F family, but with more memory (16kb ... 32 kb)

Any suggestion ?

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

Search the forums, there are many posts on this.
Usually the transition is seamless and offers a lot of benefits. The main thing to look out for is PIC18's higher interrupt latency.

dyeatman · Joined: 06 Sep 2003 Posts: 1934 Location: Norman, OK

Just curious, why did you not like the 18F242?

As a former 16F876/877 person I have worked a lot with the 252 and 452 and had virtually no problems. I had only one issue with the 4xPLL but there was an easy solution and it wasn't a fault of CCS.

Guest · Posted: Thu Sep 23, 2004 6:22 pm

Dyeatman,

First, 16F88 admints RS232 stable connectios using internal oscillator (1, 2, 4 or 8Mhz), and 18F252 does not. You have to attach a cristal to it for doing so.
Both have 10bits ADC, hardware i2c, spi, PWM and same amount of EEPROM.
So, apart from other "little" differences, the most important are 32kb of program memory and 1,5kb of RAM.
Would like an 16F89 or 16F90 with 16kb or 32kb.

Bye, bye.-

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

Well, the differences are more than 'a little'. Aside from more RAM and FLASH as you mentioned, you also get
-Enhanced EEPROM & FLASH with better endurance
-Higher operating speed
-Timer 3
-Priority level interrupts
-More interrupt sources
-Hardware multiplier
-RS485 support
-Continuous data and program memories, no more banks/segments
-Faster ICSP programing

And many more I have missed.

bdavis · Posted: Thu Sep 23, 2004 7:05 pm

Most of the 18Fxxx devices also have single cycle multiply - very nice. If you use the latest compiler, most issues are minor and can be easily worked around. In looking for a 18 pin PIC, they have a 18F1320 - only 4 K of memory, and no hardware I2C. I think Microchip is working on the high volume first, then later will have 16K or 32K chips in low pin count. You can look on future products to see what they have planned - I don't have time at the moment. I do wish they had at least 8K or 16K in a low pin count package (16Fxxx or 18Fxxx).

The paging is a bit easier in 18Fxxx part too I think. I would think they would extend the 16F88 to 8 KBytes at some point in the future, but since it only has a 13 bit program counter, I'm thinking that 18Fxxx must be used for anything over 8K. I wonder when they will have a PIC12Fxxx with a couple of megabytes? (just kidding)

Guest · Posted: Thu Sep 23, 2004 8:46 pm

Haplo !

Seems you haven´t already read 16F88´s datasheet.

-Enhanced EEPROM & FLASH with better endurance -> BOTH HAVE
-Higher operating speed -> 25Mhz against 20Mhz (and, wasn´t there a problem when using 18F at higher frequencies ?)
-Timer 3 -> Great for 18F ! But isn´t something you ALLWAYS would use
-Priority level interrupts -> Great for 18F ! (Sincerely)
-More interrupt sources -> Havent you read 16F88 datasheet ?
-Hardware multiplier -> Great for 18F ! (Important if you need high speed computation, but.....)
-RS485 support -> BOTH HAVE, but 16F88 has automatic 9-bit detection !!
-Continuous data and program memories, no more banks/segments -> Very important if you use assembler. NOT SO important if you use CCS compiler. (I´ve said NOT SO important)
-Faster ICSP programing -> I think you meant 16F88, didn´t you ?

And I tell you one more. You have (in 16F88) and extended WDT, with a period of up to 268 seg. This is great.

So, changing from 16F88 to 18F252, you pay more than twice the price for.....memory. The other stuff is not relevant.

I want a 16F88 with 16Kb !!!!

Bye bye.-

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

What I wrote was a simple comparison between PIC16 and PIC18 families, not a direct comparison between PIC16F88 and PIC18F452. And according to what you said some of the PIC18 features are better than PIC16s, but you don't use them. That doesn't make PIC18s bad products, just not suitable for your project.
By the way which source is charging you double the PIC16 price for PIC18s? Down here in Australia I get PIC18F452 for $7.37 and PIC16F877 for $7.43 from Arrows.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

Yes, PIC18 are better AND cheaper.
I've sent you the contact information for Arrows Electronics in a private message.

Guest · Posted: Fri Sep 24, 2004 6:46 am

Haplo,

I am comparing 16F88 against 18F252. I am not comparing 16F against 18F family.
You are comparing 16F877 against 18F452. And this is another story.

On prices, this is what you get buying 25 units:

16F88 --> $2,60
18F252 -> $ 5,44

Just what I said.

Maybe you didn´t catch it, but I was looking for a 18F micro -that wasn´t a 18FX52- wich would be "stable", not pricey, with similar cababilities of 16F88, and with more program and data memory. Anyone would help ??

Bye bye.-