topic Re: which one to use in 8-bit Microcontrollers

which one to use

airswit — Wed, 10 May 2006 14:10:32 GMT

Hi, I was wondering if you could help me choose a simple 8 bit micro. I want to design a simple system, one that debounces a pushbutton, and then and upon the first press, it signals a voltage regulator to turn on, for the rest of my system. this micro will also be sending a signal to my main processor when the next keypress happens (power down). The main processor will then send a signal back to this 8 bit micro to tell it to go ahead and shut down the voltage regulator. so basically, it needs:

an input for the switch
an input from the main processor
an output to the main processor
an output to the voltage regulator

Also, I wouldn't mind it to have its own voltage regulator, oscillator, and hopefully some sort of timer as well (not watchdog).
Low power modes would be nice (if i could scale down the internal oscillator, this would be good), since most of the time the proc will be idle. I will likely only need to be operating in the 10s of kHz range, no need for anything faster.

I would also like the development tools (cables,software,etc) to be cheap.

any suggestions? are there any app notes out there that covers a topic similar to this one?

thanks in advance,
Trevor

Message Edited by airswit on 05-10-200602:34 AM

Re: which one to use

peg — Wed, 10 May 2006 15:08:40 GMT

Hi Trevor,

I see you online so I quickly suggest QT1, s08QG4 or new RS08.

Regards Peg

Re: which one to use

yb — Wed, 10 May 2006 15:57:55 GMT

Hi,

9S08QG4 in SO8 or DIP8 package is the best choise.

There is no need to external components except the power regulator.

But a zener + resistor can be ok.

You can select the bus frequency by software and the 9S08 family have several STOP mode tu reduce power consumption. In STOP modes, the internal oscillator is off. The push button can be reactive the chip (IRQ pin for example)

For the developpement, CodeWarrior for HC(S)08 + P&E Multilink BDM.

Regards

Re: which one to use

airswit — Wed, 10 May 2006 22:40:43 GMT

well, i need to do some more research, but the 9S08QG4 seems to be close to what i need. however, i was wondering if you could tell me if there is the possibility to interrupt from two external sources (the pushbutton and the main processor), because I would like to be in stop mode the whole time, unless the system 'changes state'.

Thanks again,
Trevor

Re: which one to use

UK_CF_FAE — Thu, 11 May 2006 03:10:04 GMT

Hi Trevor,

You asked about external interrupts waking up the MCU from Stop mode.

Well, the QG4 has a module called KBI - Keyboard Interrupt. The MCU can be put into Stop3 mode, and woken up by any of the kBI pins - these are shared with PortA.

I refer you to chapter 3.6.6 and Chapter 9 in the datsheet.

Good Luck,

Mark

Re: which one to use

airswit — Thu, 11 May 2006 05:16:53 GMT

for some reason i am not finding anything about the keyboard pins in the datasheet at http://www.freescale.com/files/microcontrollers/doc/data_sheet/MC9S08QG8.pdf

is there a different datasheet somewhere?

also, which pins would i hook up the BDM cable to? would I have to do any multiplexing or jumpered settings on the pins?

Re: which one to use

peg — Thu, 11 May 2006 06:07:23 GMT

Hi,

Try Chapter 12 (page 173) of MC9S08QG8.pdf Rev. 1.01 10/2005

The BDM connects to power, BKGD and RESET.

If you use these pins as inputs in the application and they are coming from "off board" this may make the dual use easier/safer. Another idea is to use a QG8 for development and use a QG4 in the end product. Makes like easier, I have done this a few times with QT/QY.

Regards Peg

Re: which one to use

airswit — Thu, 11 May 2006 09:57:37 GMT

thanks for the reply peg. I don't know if i was looking at a different datasheet yesterday, but right after my last post, i found the section i was after (kbi). Now, from what i have read, the KBI works just like a regular interrupt port? meaning that just a transition on the pin signals an interrupt? what i am wondering is whether these pins are used to make an 'array' of keys. aka, if there were 6 kbi pins, could i have a grid of 3x3 buttons, or is it mapped 1 pin for every switch?

Re: which one to use

peg — Thu, 11 May 2006 10:14:20 GMT

Hi,

A matix keypad is just one use for the KBI pins.
It is very general purpose though.

If you just enable one pin of the port as KBI then it just works like a IRQ but with a different priority. Once you enable more than one, as there is only one vector, it is up to you to work out which one generated it and handle the cases where one is still active from previously etc.

All in all, the applications for the KBI are only limited by your imagination and programming skills.

Regards Peg

Re: which one to use

yb — Thu, 11 May 2006 13:49:48 GMT

Hi,

If you want very low power mode (STOP1), KBI can't exit from STOP...
KBI can only exit from STOP3.

Regards,

Re: which one to use

bigmac — Thu, 11 May 2006 14:34:31 GMT

Hello Trevor,

Since the main processor is powered down for some of the time, yet you also require the main processor to interrupt the new device, this may present a minor difficulty. It would seem that you would need to buffer the output from the main processor with a NPN bipolar transistor or N-channel FET. The transistor would conduct to generate the interrupt, but there would be no additional current draw when the main processor was powered down.

Regards,
Ewen

Re: which one to use

airswit — Fri, 12 May 2006 05:41:23 GMT

now, one last question. Is there any way (without writing a lot of software, no time) to program this chip using my M5213evb? that would be awesome!

another quick question: can the development board be used to program the 8 pin device? it appears that all the pins line up, at a glance, but i was wondering if any of you knew for certain ($50$100, right?!)

thanks,

trevor

Message Edited by airswit on 05-11-200606:12 PM

Re: which one to use

yb — Mon, 15 May 2006 14:28:12 GMT

Hi,

For your development, you can use the QG8 DEMO BOARD.

After, to program your final app, you will use the BDM which is on the demo board with a 6 ribbon cable.

You can program other ref than QG8 with this BDM : I tried with a GB32, and it worked.

Regards,

Message Edited by yb on 05-15-200610:30 AM

Re: which one to use

airswit — Mon, 15 May 2006 22:08:04 GMT

thanks yvan,

i wasn't sure if the development board was able to drive signals from the bdm cable header. so now, i am wondering: why is it that the BDM cable costs more then the development board, if you can use the development board to program other procs?! either way, no matter...

thanks again,

Trevor

Re: which one to use

peg — Tue, 16 May 2006 05:35:42 GMT

Hi all,

The subject of using a QG8 demo board to progrogramme/ etc other devices has been discussed extensively before (I will let you find it!). It appears to work perfectly. The price diffence I think you will find is:

1: No sexy blue/purple box

2: Marketing deciding that they can forgo some profit on these in order to sell millions more QG8's in the future.

Regards Peg

Re: which one to use

rhinoceroshead — Tue, 16 May 2006 10:29:35 GMT

Okay Peg, I looked for the thread but didn't find it - but I was only scanning the thread titles.

Anyway, let me guess - you can get the BDM on the QG8 demo board to program other devices only if you remove the QG8 PDIP? Is that correct? The only reason I'm asking is because I tried to do that on the S12XDT512 board which has a SMD uC there. I was thinking that it should work if I could prevent the DT512 from getting powered up - so it wouldn't answer the BDM calls. If memory serves, I think I concluded that the only way to make it work would be to cut traces on the board.

I bought the USB-ML-12 and never looked back. :smileyhappy:

I always wondered why they would stick that BDM port there if it wasn't intended to program other devices. It just seemed unlikely that somebody would use that since the USB programmer was right there. I guess that's why it was not populated...

Re: which one to use

peg — Tue, 16 May 2006 10:55:41 GMT

Hi,

My memory is better than I thought. It was back on Freegeeks. You remember.... the forum where the forum stuff actually worked... like searching and code posting boxes...........

Anyway enough stirring here are some links:

http://forums.freescale.com/freescale/board/message?board.id=8BITCOMM&message.id=265

http://www.freegeeks.net/modules.php?name=Forums&file=viewtopic&t=459

yes, the main reason it works is you can pull the DIP part out of the socket!

Regards Peg

Re: which one to use

rhinoceroshead — Tue, 16 May 2006 11:38:40 GMT

Hmmm... That means that the QG8 is the one and only demo board with both a PDIP socket and a BDM host - and it's cheap. Could it be a mistake? On any of those other DEMO boards it would have been really easy to make it serve as a BDM POD, but they chose not to do that - I assume because they wanted you to buy the Multilink cable.

I didn't find out about the freegeeks.com forum until it had already moved here. I wish I had known about it 3 or 4 years ago when I was learning this stuff. Maybe then I would still have hair. :smileyhappy:

Re: which one to use

Wings — Tue, 16 May 2006 18:52:42 GMT

If you're about to decide on the 4-pin QG4 over the 16-pin, one thing you may want to consider is that the 4-pin does not have the Debug Module like the 16-pin chips (and I think ALL the other S chips). This will limit you to only having 1 breakpoint to use (rather than 3), and no trace functions.

I think the cost difference between these 2 chips is just a few pennies.

Re: which one to use

Alban — Tue, 16 May 2006 19:30:23 GMT

Hey Rhino,

Sorry to hear about your hair, but freegeeks.NET is not that old.

I participated to its launch last year.

Sometimes the landlord of the site (freegeek) is coming round here but he's a busy man...

Don't think your hair stood a chance...

Alban.