[Simh] VAXELN, rtVAX-1000, WTC, time

[Johnny Billquist]

Not really. :-)

This gives the technical explanation on how the system works. Bottom 
line is that you have a TOY clock, and it continues working even with 
power off. The battery is just the power source of the TOY when main 
power is off. What is needed to be understood is how the TODR register 
works.

And to clarify things more to the OP, the TOY is then responsible for 
updating the TODR. So TODR should always continue counting even if power 
is off. So if you always see low values, it would seem that it gets 
reset at some point.
The TODR have no further meaning. It is just a free running counter 
incrementing every 10 ms. It's up to the OS to do something clever with 
it. I don't remember exactly how VMS or anything else use it, but it is 
used in combination with some information stored in the file system to 
figure out what the current time is at boot.

   Johnny


On 2018-12-15 22:25, Wilm Boerhout wrote:
> 
>> The few actual reads of the TODR during ELN's execution are returning low values (since nothing actually set the clock yet).
>>
>> Do you get the same result if you don't attach the CLK device?
>>
>> If the result is the same, then it would seem that ELN doesn't care to use the hardware clock for much of anything.  Maybe there is some setting within ELN that could influence more direct use of the clock.
>>
>> - Mark
>>
> This from the rtVAX 1000 System User's Guide (1985)
> 
> When the system is off, the battery backup unit (BBU) (internal) provides
> power to the time-of-year (TOY) clock chip on the KA620-A. The code for
> the user's language is stored in RAM on this chip and is lost if the BBU 
> fails.
> 
> For more information, see the rtVAX KA620A CPU Module User's Guide
> 
> That guide is not to be found on line. So what we're really looking for, 
> is a battery. :-)
> 
> 
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Johnny Billquist                  || "I'm on a bus
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