Driving an 8 digit 7 segment LED from a setup meant for two COP470s - Page 1
Forum section: electronics / general

author: turbo!
author_rank: Regular Contributor
timestamp: April 20, 2014, 08:44:28 am
content: So, I've got a micro controller driving two National Semiconductor COP470s driving an 8 digit numeric display. The SA-SH segment outputs are tied together and the digits 1-4 are driven by chip 1, 5-8 by chip 2.Can I drive an 8 digit 7 segment LED display using the signal from this controller using a MAX7219?Input is tied electrically except the chip select. Each chip gets its own CS input from the controller. How do I tie the two CS outputs from the existing signal source? Can I simply wire them in parallel?Currently, it is hooked up like:microcontroller-chip1-chip2SO-DI-DISK-SK-SKDO-CS(chip 1)D1-CS(chip 2)

author: dannyf
author_rank: Super Contributor
timestamp: April 20, 2014, 11:30:56 am
content: Quote1. anything is possible, particularly if you have access to the mcu.2. it is unlikely to work with the max7219 if you don't have access to the mcu. The max7219 requires set-up to turn on the leds, and the COP370 has some peculiar ways of driving the leds.

author: turbo!
author_rank: Regular Contributor
timestamp: April 20, 2014, 03:13:40 pm
content: Quote from: dannyf on April 20, 2014, 11:30:56 amNo, I don't have access to upstream of the display unit, which is assembled with two COP470s and a VFD. Attached is a datasheet for COP470, which I don't really understand all that well.What modern single IC setup can drive a 7 segment 8 digit LED using existing data bus? What the hell is "microwire" compatible?

author: dannyf
author_rank: Super Contributor
timestamp: April 20, 2014, 03:33:35 pm
content: QuoteIt is very confusing here. I thought initially that you didn't have the display unit and are looking for max7219 to interface with your existing "mcu".Now, it looks like you have the display unit but are looking to drive it? If so, why do you need a max7219?All you need is a mcu to send the display unit data.I guess before you move forward, what exactly do you have and what exactly are you looking to do?

author: turbo!
author_rank: Regular Contributor
timestamp: April 20, 2014, 03:42:36 pm
content: The "display unit" is.Plugging in an identical display unit from another working unit makes it work, but that one went back to that unit.By having no access to MCU, I meant that I can't invoke any type of modification like coding change to the main board, which provides the signal to the display assembly which as shown in the diagram is to the right of COP 400. As long as the signal is compatible, piggy backing a 3 terminal regulator somewhere is within the realm of what I can do.So, I need to be able to interface the output of existing MCU which splits into CS1/CS2 and into driving a MAX7219 which do not use the same input type.

author: dannyf
author_rank: Super Contributor
timestamp: April 20, 2014, 03:50:05 pm
content: It is doable but fairly involved.If I were to do it, I would put a mcu there: your mcu will digest the information sent by the upstream mcu and then decide how / what information it will send to its own display unit, max7219 or not.It will not be easy to do this - the COP370/470 has an interesting way of driving leds. If your unit doesn't follow that, you will have to figure how it works first and then write your code to essentially clone a COP370/470.

author: turbo!
author_rank: Regular Contributor
timestamp: April 20, 2014, 04:14:54 pm
content: Quote from: dannyf on April 20, 2014, 03:50:05 pmI thought its more or less a standard multiplexing VFD drive method?The digit grid voltage is on, on standby, and off when on but that's just the way VFDs work.

author: edavid
author_rank: Super Contributor
timestamp: April 20, 2014, 09:52:05 pm
content: Microwire is a predecessor of SPI:http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus#MicrowireIf you wanted to learn about microprocessors, this could be a fun project for you, but probably the simplest solution is to order some COP470s from China:http://www.utsource.net/cop470.html

author: turbo!
author_rank: Regular Contributor
timestamp: April 22, 2014, 01:23:24 pm
content: Quote from: edavid on April 20, 2014, 09:52:05 pmSo can I use the 7221 instead? It says in the datasheet that it is fully compatible with SPI, microwire, etc.

author: dannyf
author_rank: Super Contributor
timestamp: April 22, 2014, 01:30:49 pm
content: QuoteRead the COP370/470 datasheet and then 72221 datasheet and you will know how those devices are driven and then the answer will become clear to you.You have to learn to read and understand a datasheet and now is better than ever to do that.

author: turbo!
author_rank: Regular Contributor
timestamp: April 22, 2014, 05:18:43 pm
content: Quote from: dannyf on April 22, 2014, 01:30:49 pmYour explanations are lacking. "look at the datasheet, you should know".if it was self-explanatory to me, I wouldn't bother asking and your explanation isn't getting me understanding it one bit further.

author: edavid
author_rank: Super Contributor
timestamp: April 22, 2014, 05:43:14 pm
content: Quote from: turbo! on April 22, 2014, 01:23:24 pmNo.

author: free_electron
author_rank: Super Contributor
timestamp: April 22, 2014, 05:56:59 pm
content: @turbo. lemme guess. your basic understanding of electronics is very low. I'm not blaming or calling you names. just an observation.The forum is used to people with a lot more experience so , if you do not explicitly state that you are a 'beginner' ( not a bad word, we were all begineers ) you tend to get answers like the last few.it is clear that you have little experience with these things.Microwire is a communication bus. having a chip say it is compatible with the bus means nothing towards the software. each chip has unique instructions. so you cant swap them. besides chips can have different functionality you can have memories, display drivers, relay drivers , radio tuners, all in microwire.so, in short , only a cop470 can replace a cop470. these chips are very old. nobody made a second source. when National semiconductor spun off their digital stuff to fairchild these chips died. (went out of production)so you have two options1) find a few on ebay (there's plenty) , hook em up to display and off you go.2) make your own. ideal job for some logic. Microwire is nothing but a shift register. fits easily in a small cpld , hook up dsiplay of your choice.given your lack of electronics skills only 1 is a true option for you.you could attempt 2 but be prepared for some steep learning curve. it may take multiple months to learn the necessary basics.

author: turbo!
author_rank: Regular Contributor
timestamp: April 22, 2014, 07:35:15 pm
content: I have electronic experience. Just no coding/software stuff.

author: dannyf
author_rank: Super Contributor
timestamp: April 22, 2014, 07:48:06 pm
content: QuoteYou can probably broaden your horizon there a little bit.