[time-nuts] 59503A GPIB clock windows/linux software.

[Hal Murray]

tvb at LeapSecond.com said:
> The hp 59309A has a talk-only mode where timestamps are output at 40 Hz; so
> that would narrow it down to 25 ms.

You can get (much?) better than 25 ms if the timestamps are locked to the 
master clock or PPS.

If not, you can also get into hanging-bridge type adventures.  :)


> BTW, if you're curious, look at the service manual (http://ko4bb.com/
> manuals.php). This is a pre-microprocessor age GPIB instrument that uses a
> 4096-bit ROM-based state machine (A5U2) as a CPU. Very clever, very 70's. 

I was designing hardware back in those days, and writing microcode too.  The 
good old days really were "good", at least in my memories.

If you get more than ballpark of 20 states in your state machine, it's often 
simpler to think of the problem as software rather than hardware.  That 
probably works better if you have some experience writing microcode.

At the hardware level, for the gear I worked on, each instruction had a 
next-PC field.  One trick was to implement branches by ORing bits into the 
bottom bits of the next-PC.  The assembler did most of the work.

For anything bigger than roughly 20 states, we would write a real assembler.  
That's not a lot of work if you start from a previous example.  Just change 
all the keywords and matching dictionary.

4096 is 512x8, 9 address bits and 8 data bits, so you get X bits of PC and 
9-X bits to branch on.  You can get more branch bits by using a mux keyed off 
some high-order PC bits or something like that.  (That's more work for the 
assembler, but the programmer doesn't have to think about it.)





-- 
These are my opinions.  I hate spam.