RTC Module Replacement



Dallas DS1287 DS12887.jpg



Although Dallas and others made newer model RTC modules that can be used as substitutes for obsolete RTC modules (such as the DS1287), you cannot always use the new model RTC modules as a 'drop-in' substitute.

The three documents below discuss some known substitution problems.

Maxim (Maxim Integrated Products, Inc.) acquired Dallas Semiconductor in 2001.



Some documents that discuss some known substitution problems

Year Document
2002 Dallas/Maxim - Application Note 503
? Dallas - Application Note 521 - Replacement for the MC146818
2005 RTC Module (Dallas Semiconductor, et al) FAQ
2009 Real-Time Clock (RTC) FAQ



Depleted battery

Some replacement modules contain a battery.  The DS12887 is an example.  Such modules, found on eBay and elsewhere, possibly contain a dead (or well depleted) battery.



Some (repeat:some) known compatibility/incompatibility

Computer Supplied with  Compatibility / incompatibility
Compaq SLT/286 DS1287 Cannot be replaced with DS12887.  See here.
Dell 316SX DS1287 Cannot be replaced with DS12887.  See thread 55621 at the Vintage Computer Federation Forums (in that, posts #24 and #25).
IBM AT (IBM 5170) MC146818P As discovered by member 'rodney' at the Vintage Computer Federation Forums (and verified by 'modem7'), a DS12885 can only replace the MC146818 if pins 16 and 20 are disconnected from the motherboard, and a 3 volt battery connected to those pins.  See here for a photo of my test.
IBM PS/1 model 2011 DS1287 Can be replaced with DS12887A+.  See thread at here.       (The plus denotes lead-free.)
IBM PS/2 model 30 286 DS1287 At post #17 of here at the Vintage Computer Federation Forums, a Glitch Works GW-12887 was successfully used.
IBM PS/2 model 35 SX DS1287 See thread 59447 at the Vintage Computer Federation Forums
IBM PS/2 model 55 SX DS1287 - See thread 13830 at the Vintage Computer Federation Forums
- See thread 1247646 at the Vintage Computer Federation Forums
Tandy 2500XL DS1287 ? Can be replaced with DS12887A+.  See post #7 at here.       (The plus denotes lead-free.)


Motherboard Supplied with  Compatibility / incompatibility
Octek FOX II 286 HM6818P On this motherboard, the HM6818P can be replaced with a nwX287.  See the thread at here.



Some (repeat:some) known other issues

Item  Issue
Motherboard with 430nx chipset Various issues are discussed at here.