Discrete Logic vs. µController
Nick McClick
Posts: 1,003
What's the practical advantage to using Discrete Logic instead of a µController? A few I can think of:
- Price - although if an attiny replaces 3 or 4 discrete logic chips, it seems like a wash
- Switching speed? How many instructions per second would be required to keep up?
- Development time, maybe?
Anything else?
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- Price - although if an attiny replaces 3 or 4 discrete logic chips, it seems like a wash
- Switching speed? How many instructions per second would be required to keep up?
- Development time, maybe?
Anything else?
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Comments
That's what I think separates the two, although I personally prefer microcontrollers.·
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3.1415926535897932384....
Dynamic re-programmability.... what if you got your discrete logic wrong, or simply needed to change it based on the circumstance?
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
I am in the middle of an issue like this working to restore an odd 24 year old CPM system which used quite a few custom PLD devices and unfortunately the data to recreate them has been long lost. If regular logic has been used it wouldn't be a problem. Of course the chip count would be higher so there is a downside to that method too.
Robert
No, I'm pro-µController, I'm just wondering if there's any need to stock some of the discrete logic chips I carry, or if their function can be emulated with a µController.
Re: development time - makes sense if you're trying to compress several logic chips into a single IC, but what if you're just doing a drop-in replacement for a decade counter?
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I frequently employ the ATTiny13 in circuits that require few I/Os and a lot of "smarts". At less than a dollar each in quantity, it can be a good choice. For example, I'm currently working on a simple board that interfaces to a BASIC Stamp. It wouldn't necessarily have needed a microcontroller, but including one enabled the interface to be serial, connected by a three-pin servo cable. Without the micro, A six-pin cable and a more expensive sensor chip would've been necessary. By the time you figure the extra cost for connectors and cabling, the ATTiny looks like a bargain. Moreover, I can add functionality that would have been impossible without it. Plus, it's much easier to program in-circuit than a PIC. (I use a MoBoStamp-pe and a short cable with an 8-pin SOIC clip at the end.) Finally, if you need an ADC, the ATTiny, with it's own multiplexed 10-bit ADC, is cheaper than most dedicated units. (The architecture takes some getting used to, though.)
But if you need fast logic with lots of I/Os, 74HC discrete devices are the better choice. Typical circuits will include 75HC595s and/or 74HC164s for I/O expansion. I also make use of single- and dual-gate 74LVC devices in SOT23-5 and -6 packages. These are handy for localized logic functions and are small enough to be placed where they're needed.
Now that the Propeller's price has been cut, it's also a real value proposition for replacing high-functioning logic and peripheral devices. With 28 usable I/Os and a small footprint, it can replace an entire boardful of stuff, reducing the overall size and cost. I would argue (and have demonstrated) that the Prop can easily fill in for dedicated peripheral chips at a reduced cost and with enhanced flexibility.
-Phil
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
The high speed discrete logic chips have advantages, but there aren't a lot of DIP versions of those chips, so it's a moot point.
Cheapo ucontrollers work fine for most applications.
Everything is a trade off, but I prefer to it make it easier for the builder and to stock less components.
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· -- Carl, nn5i@arrl.net
Yea with 8$ a chip that is only a dollar a core. Cant go wrong there. Unless you need it to have dedicated ADC.
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
The steady hands game I did (photo's should be in completed projects) had one descrete chip acting as a latch as the·BS2 does not have one. It was cheep enough to dig through my 'surplus' draw and find something that worked. This is stocked by a grab-bag of surplus logic parts.
I wouldn't use a micro-controller·if all I needed was·a J-K flip-flop for example, but could emulate one·if I'm comitted to·using a micro-controller that has edge-triggering. A recent project I put together,·I added a couple of latches to extend·number of·output bits·(grab-bag material) and a·64K RAM (grab-bag material) combined with an SX28.·I·then looked at the most optimal way of putting all these together·without eagerly adding additional chips.
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