8-bit Microcontrollers中的主题 Re: MC908QB8 - apparent discrepancy between datasheet & parametric search

MC908QB8 - apparent discrepancy between datasheet & parametric search

Smiffytech — Sat, 28 Feb 2009 18:22:03 GMT

I have before me a MC908QB8MPE.

The datasheet for this states in part 1.1, General Description, Summary of Device Variations:

MC68HC908QB8 - 16-Bit Timer Channels: 4.

Today I chanced to look back on the site to get an idea of current cost; when I found the device that I had on the parametric table, it has this to say on timers:

# timers: 1; timer channels: 1; timers size (bits): 10.

As the datasheet I have on my machine is a couple of years old, I downloaded the one from the link right next to the appropriate part on the parametric page. Same datasheet.

Would someone be so good as to enlighten me as to what exactly is going on here? It looks like something has either been written in an unclear/confusing manner or maybe just plain incorrect.

I'd really like to be told that the devices I have do have 4 timers - I've got a really cool synthesiser design in which these would work beautifully. (I'll be Open Sourcing the design if the prototype works out. Will post a link here, of course.)

Re: MC908QB8 - apparent discrepancy between datasheet & parametric search

bigmac — Sat, 28 Feb 2009 20:29:58 GMT

Hello, and welcome to the forum.

The current datasheet for the device should be your primary reference. Datasheet errors do occur from time to time, but there is more chance of any errors being corrected within the next datasheet revision.

For the case that you mention, the '908QB8 definitely does have four TIM channels.

Regards,

Mac

Re: MC908QB8 - apparent discrepancy between datasheet & parametric search

Smiffytech — Sun, 01 Mar 2009 05:23:01 GMT

Many thanks for that, clarification much appreciated.

The device is therefore still perfect for my "Nitron Organ"*, so I'll soldier on with the design.

How do I go about reporting an issue with the parametrics table? I tried selecting the floaty 'feedback' thingy but just got an empty white rectangle that wasn't much help (not tested with Firefox, methinks.)

Cheers

* 1 device as assigner/arpeggiator, 1 device as primary oscillator with 4 octave outputs (that's why I wanted the 4 timers), 1 or more devices as detunable secondary oscillators. Then possibly 2 more devices as LFOs. All the rest is analogue. Distributed computing rocks!

Re: MC908QB8 - apparent discrepancy between datasheet & parametric search

bigmac — Mon, 02 Mar 2009 07:25:15 GMT

Hello,

Keep in mind that there is only a single TIM module that shares a common prescaler for all four channels. Assuming a prescale value of 1, and a bus frequency of 3.2MHz, you would be limited to a period resolution of 0.3125 us. For a top octave square wave, say 3 octaves above concert A, the frequency resolution would be 3.9 Hz (~2 cents), probably OK for your requirement.

To use output compare mode to generate a square wave, the half-period of the output waveform may not exceed the timer overflow period, 20.48 ms for the above example. This will provide a lower limit for notes generated simultaneously with very high notes.

Regards,

Mac