RTC Module and Arduino to simulate vintage RTC?

So i am an avid collector of older computers and of course many of them come with dinosaur real time clocks installed. I have thought maybe it's possible to simulate an older real time clock module for pinout configuration so that a Arduino could be used in place of the old RTC chip.

I know RTC's rely heavily on a very calibrated crystal to keep accurate time. I was wondering if I could use a new RTC module for the Arduino with battery backup to keep accurate time, but declare the cert pins on the Arduino to be used as the original RTC module like the 5 address lines, 8 data lines, Write enabled, etc..

If so, then a small PCB can be created to plug the arduino onto and that PCB can be plugged in place of the vintage RTC chip. Boot code would access the arduino RTC to get the time and date as normal. The vintage computer would use its programmed logic to access the arduino simulated RTC through the declared pins.

Anyone have any experience with such a project or even think this is possible?

Why do you want to replace the relativly new RTC chip ?

Short answer is absolutely yes. Just look at the original datasheet and write an emulator one step at a time.
This would be a project worth showing off too.
@Retroplayer check this out.

As far as I know there are no dinosaurs allive and working, but no doubt there are a great many RTCs from the relativly recent recent PCs still working.

Cannot quite remember when the RTCs first came in, in my early days I well remember having to set the data and time manually on XTs ana ATs.

Are you talking about the Dallas Semiconductor DS1287? The 'RTC Chip' with the sealed-in battery? Or is there a chip from the 70's or 80's that didn't work properly after a certain date? In what other ways are the old-school RTC chips failing?

@shift838 I think that is entirely possible and sounds like a nice project.

You will probably have moments in the middle where you wish you hadn’t embarked on such a venture, but the result will be worth it.

I’ve just received some of the little MEGA Arduino boards, lotsa real I/O pins to use, which you def don’t want to need to do otherwise.

Also learn up direct port access, it will simplify the simulation of the various signals I think, and make getting the timing easier.

I have some devices with DS whatever it was with the sealed in battery, they outlived their specified life time by a good stretch but are now failed. I have seen recipes for cracking them and replacing the battery…

All depends on what kind of fun you want to have. :expressionless:


The older IBM and similar PCs only looked at the battery backup clock chip at boot time. After that all time was kept by software.

How accurate do you figure that software timekeeping was?

About as accurate as current RTCs.

And of course before that they always started up on a Tuesday.

Cool. I would think they would like to eliminate any little software task like that, but perhaps I am misunderstanding how it was achieved.


Of course they enjoyed the advantage of needing to be rebooted about twelve times a day.


1 Like

Nah, that did not become common until Windows Millenium.

1 Like

Simply, the clock chip just died. I had 2 that died. They do have sealed batteries and I did do a Frankenstein surgery on one of them (Frankenstein Clock Surgery) and got it working with no issue, but I thought i wonder if I could do this with an arduino and a newer serial clock module.

I also have a clock chip (MM58167AN - it's a 24pin DIP) that died (no internal battery or crystal) it's just dead. I do have spares but I would really like to try and get an arduino replacement for this one.

I've done arduino coding for projects like my MIDI Foot Controller that controls my recording software and such but nothing like this where I need to simulate pins and then reroute whatever is needed. Not sure how to even do that yet..

I suggest you need to first see if the BIOS will accept your substitute.

this is a super old computer. no bios. We are talking about a TI-99/4A made in 1981

If he does what I think he means to, there’s no way the BIOS woukd even know.


Ah I see, whiy did you not say ?

So I presume you mean the modern Dallas RTC devices failed ?

the one i want to target first is MM58167AN

This chip has 5 address lines and 8 I/O lines. I would like to use maybe a Arduino Nano for it.