Paul, Interesting you should point this out as the PICTIC was a spin-off of a 5-year effort to modernize the Shera controller for my own use. The 42ns TIC in the Shera was a weak point and a different TIC with higher resolution was needed if sawtooth correction was desired. My GPSMAX controller uses a smart divider to supply a synchronized 1PPS to the panel and a delayed 500K to the PICTIC front end allowing the 1PPS timing to be varied by adjusting the controller setpoint. Just the TS274 portion of the PICTIC II interpolator is used for a gain of 400 with the gain reduced to 100 to give 1ns resolution. Over 100 serial commands allow remote operation and monitoring over a serial link, and all process variables can be displayed or adjusted on command. Accumulation times of 30, 60, 120, and 240 seconds were added for higher stability sources. Accumulated sawtooth data from a Motorola GPS is used to correct the accumulated TIC value prior to subtracting the setpoint and sending the error to the Shera filter. The filter output passes thru a scaler and is added to a correction register, then the correction register value is sent to a 23-bit DAC similar to the 22-bit design used in the SRS PRS10 Rb. The correction register can be loaded directly by serial command to set the frequency offset, eliminating the offset trimmer and associated loss of sensitivity and noise pickup. The scaler allows loop gain adjustment for differing oscillators by software command without changing resistors and allows a direct to DAC connection for many oscillators. A temperature sensor and 1PPS fail detection were added along with age and temperature compensation in holdover. The direct to DAC connection and the higher resolution of the interpolating front end adds sufficient gain for use with most Rb sources.
Richard > In message <[email protected]>, Bruce Griffiths writes: > >>Instead of copying the Shera controller albeit with higher resolution >>its probably more cost effective to choose a microprocessor with built >>in time stamping capability. > > Uhm, isn't this exactly where you want to use the > still-smelling-like-brand-new-car PICTIC II with a good DAC and > a microcontroller ? > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [email protected] | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
