I created this to replace a dead Dallas DS1287 real time clock in my IBM PS/2 Model 55 SX, though there are a number of systems that can use these. There are three versions available:
- Dallas DS12885
- Benchmarq bq3285
- Benchmarq bq4285
The Dallas DS12885 is functionally compatible with the DS12887, DS1285 and DS1287.
The Benchmarq bq3285 is functionally compatible with the Benchmarq bq3287, Dallas DS1285 and DS1287. Functionally there are no real differences between the Dallas DS12885 and Benchmarq bq3285 (Benchmarq advertises a 160 nanosecond cycle time for fast bus operation).
The Benchmarq bq4285 is functionally compatible with the Benchmarq bq4287, Dallas DS1285 and DS1287 (will work as a replacement for the DS12887, DS12B887, and Odin OEC12C887). This chip seems to have the least compatibility with the DS12887.
These use a CR1220/1225 battery, one is included and these are widely available online.
The modules are ~1mm taller than a stock Dallas RTC. The optional cover adds a total of ~2.25mm.
The *85 chips are just the RTC chip, while *87 modules are the chip in an encapsulated package with the battery and crystal. So a DS14285 with a crystal and battery is the same thing as a DS14287 (which was compatible with the DS1287, which was a DS1285 with a crystal and battery). Dallas (and others) made many direct replacements for the DS1285/DS1287 (e.g. the DS14285 and DS12885). For most use cases the bq3285 is the way to go because it offers the lowest price and high compatibility. Functionally these should all be interchangeable if you're replacing a DS1285/7, but from what I've read on various forums, some people have luck with one model over another. I offer free returns if a part doesn't work out for your application.
Feel free to send me a message or leave feedback if this works for your system and I'll add a note to the auction.
If your RTC module is soldered to your motherboard I can desolder it for you and replace it with a socket if you're not comfortable doing that yourself. Just send me a message.