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Atari PC1 Real Time Clock


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While working on the PC1 ISA expansion project I spent some time reviewing the work done by @Bumzyman and looking at the pictures he shared in his gallery.  This one caught my eye:

 

 

The ROM BIOS chip has been inserted into a Dallas DS-1216E real time clock chip.

 

These were popular back in the late 80s as a way to easily add an RTC to an XT-class computer by installing them under one of the BIOS ROM chips.   Variations were also made for other popular micros.  On the PC, a popular retail package was called "SmartWatch" and it included an executable you could place in the autoexec.bat to set the system clock from the DS-1216E upon start up.   The same executable could be used to set the time which would then be maintained when the system was powered off by the 3V battery encased inside the IC.

 

Alas, as many Atari Falcon owners know, the Dallas clock chips have a major flaw.   The battery is not replaceable.   The ICs are no longer produced, and although you can still find them on a number of online trading sites, any you find today will have long dead batteries, even if the date codes have been altered to make them seem newer.

 

Dallas Semiconductor does still make timing ICs though.   The DS-1315 is an updated version of the DS-1216 timing chip that was at the heart of the DS-1216E.  Coupled with a 32.768Khz oscillator and a 3V battery, and you have a re-creation of the DS-1216E.   The original Smart Watch software works just the same.

 

This project then was to recreate the DS-1216E by using the modern alternatives, and create a simple PCB to allow the circuit to be installed in an Atari PC1.  It should also work in an Atari PC2 or PC3.   The board is very compact and requires the 3V battery to be located elsewhere.  I found a button battery holder at my local electronics store that includes a solid plastic enclosure.  A piece of tape and you're done.

 

After I completed this I discovered that djos had essentially done the exact same thing for the Tandy PC line, and has also published the work.   The Djos solution uses a larger PCB which includes the battery holder, and you can buy a complete example from Tindie, although they ship from Australia so costs for North America users may be high.  That said the DS-1315 IC is not exactly cheap either.

 

The Smart Watch software can be downloaded from here:

 

https://www.brutman.com/PCjr/DS1216E.html

 

 

Git Hub with Gerber, Dip Trace project files, supporting documentation etc.

 

https://github.com/oraclejedi/ATARIPC1_RTC

 

 

Some pictures of the unit in action here:

 

 

 

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