[Coco] Battery-Backed RTCs for CoCo?

Dave Philipsen dave at davebiz.com
Sat Dec 1 01:50:51 EST 2018

Yeah, in single quantities from Digi-Key it is a little expensive but 
you can buy the whole module from China (eBay) for a buck or two.  It 
includes a NVRAM too.

400 KHz is a standard frequency for I2C bus which is a serial bus anyway 
so it might be a little tricky trying to interface it to the CoCo's 
parallel bus without some sort of I2C controller.  You could bit-bang it 
but that's kinda messy although that may be how some of the older RTCs 
on the CoCo were done.  The older Dallas Semi (now Maxim) RTCs that work 
on a parallel bus by piggybacking a RAM/ROM chip are even more expensive 
if you can still get them.


On 11/30/2018 7:40 PM, RETRO Innovations wrote:
> On 11/30/2018 5:51 PM, Dave Philipsen wrote:
>> Actually we have a NitrOS9 driver for the newer (and cheaper) DS3231 
>> chip that is so prevalent on many RTC boards available on eBay.  It 
>> is currently used on the CoCo3FPGA.  I believe that the general 
>> register architecture of the Dallas Semi chips are all pretty much 
>> the same.  It's just that the older ones were accessed in a slightly 
>> different way before the advent of I2C and SPI.
> Hmm, that one is still highly expensive, givent eh otehr I2C options 
> on digikey.  And, the 400KHz max clock is a bummer, as that means I 
> cannot interface it with the CoCo bus directly...

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