My company has a product that is currently controlled using a MC705C8A. That controller has become obsolete and there is no direct replacement. We would like to migrate to something that is similar and perhaps switch to a SMD. Do you have any recommendations for a very similar replacement or another processor we could use that will probably be around for the next 15 years. We are thinking about moving to an 8051 family processor. I know that is pretty old technology and is not very similar to the MC705C but there are about 20 companies that manufacture drop-in compatabile chips so it should be around for quite awhile.

The function of the program is fairly simple. It's basicly an adjustable timer that counts down a cycle time and monitors water level in an open pan of boiling water. The controller monitors the water level using three magnetic reed float switches and opens a solenoid valve to add water when needed. It also turns on and off the the heaters that heat the water. When a cycle is running, the heaters are on for the duration of the cycle. When the cycle is over the heaters turn off. Between cycles the water temperature is maintained at 180 deg f.

Do you have any recommendations for a controller that may be very similar to the MC705C8A or which controller we might want to migrate to? We do not currently have any hardware/software development tools so will need to purchase what is required.

The inputs and outputs are as follows:

Inputs (6):
Start button
Timer Button
Water Temperature (comparator circuit with thermister)
High water float switch (Vcc, two states, open/closed)
Add water float switch (Vcc, two states, open/closed)
Low water float switch (Vcc, two states, open/closed)
(Vcc is 5V)

Outputs (5+):
Heater control (on or off, nothing in-between. Currently an onboard opto-coupler circuit controlling three 24VAC contactors. May migrate to SSR)
Water control (on or off. Onboard opto-coupler circuit controlling a 24VAC solenoid valve.)
4 seven segment LED displays (We want to migrate to an LCD display)
Piezoelectric buzzer

LED Outputs: (All LED lights will probably be integrated into the LCD display)
Preheat LED light
Ready LED light
Steaming LED Light
Adding Water LED light
Cool Down LED light

 

Are you sure about the part number? I think it might be missing a digit. What I can tell you is that you should look for a replacement that is in a surface mount package because the DIP parts will disappear faster. You also need to consider who will be supporting the tools you want to use. I also recommend looking at a part that has at least twice as much memory resources, both program and data, as you think you will need. Lastly if you can afford to have a part with a UART on it you can write yourself a diagnostic and testing program on it that will be most useful in manufacturing and in the field. If you have some EEPROM on the device you can give each unit a unique identity that you can interrogate and or field upgrade. I have a great deal of experience in industrial systems and you can ask me anything you want about products from automation systems and networks.

 

Specifically it's an MC68HC705C8ACP

 

Specifically it's an MC68HC705C8ACP

Ah yes. that makes a great deal more sense. I am familiar with this part. Is your application written in assembly language?

 

Ah yes. that makes a great deal more sense. I am familiar with this part. Is your application written in assembly language?

To be honest with you, I don't know. I'm trying to get that information from the company that wrote the current program for this processor. I assume it was written in C. That company was recently purchased by another company and they aren't too interested in assisting us. I, personally wrote an assembly language program for this same product over 20 years ago that used an Intel 8748DH.

 

I am just beginning my quest on this project and don't really know what to look for. I've been out of this game for a long time and have forgotten quite a bit, but not as much as I was afraid I had. Am I going down the right road in looking at an 8051? It looks like Atmel has some development hardware/software but I don't really know what to look for in that area, yet. Are there simulation programs that I can use to simulate the design and program on the computer? If so, what should I look for? Back in the day, all I had for development tools was a breadboard, some wire, a text editor, chip programmer and a UV light. LOL.

 

That is too bad about the application. I kinda doubt it was written in C. There were very few (maybe none) C compilers for the processor because the stack and stack pointer were usually not large enough to support data access to stack variables. I am also familiar with the 8748 and it's red-headed stepchild the 8051. Let me know if I can be of assistance as you wad through the minefield. Good Luck.

 

If I were you, I would go for a new modern chip.

Especially if you have programmed processors in c before.

The new chips have so much more built in "stuff" and versatility. You can use one chip for many apps. in the future. And they're cheap. Plus the available programming software is extremely good, friendly and free.

 

Since the application is not very demanding, I would stick with the idea of using an 8051 derivative because of the low price, long history and excellent prospects for continued availability from multiple sources and support in the future.

Having once coded a similar timer project in 8051 then migrating it to a 68705 when the 68705 came out, the two are not all that different, mainly in the registers on the chips as the instructions are (generally) similar. Moving to something like the PIC or AVR would be a little more difficult but after all, a controller is a controller.

 

Thank you all for your responses. Do you have any recommendations on simulation/development software/hardware?

 

I paid $10 for this.

http://www.ti.com/lit/ug/slau597a/slau597a.pdf

And $19 for this.

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/data_brief/DM00094498.pdf

They both come with excellent software and many examples.

That last one has a ROM library built in.