Re: [time-nuts] A Simple PIC Divider
Hi Randy,
For most purposes seven 7490's or four HC390's or
three HCT40103, etc. will work just fine. Speaking
for myself, the main thing was parts count. And being
more of a software person than hardware I prefer a
one IC solution (which has the fun of software) to
a 3, 4, or 7 IC solution.
The other issues, which may or may not have any
bearing on some applications is that the latency
and the tempco of a multi-chip solution is likely
worse than a single IC solution.
Lastly, once one has programmed a PIC you realize
that dividing by almost any number is just as easy
as 10M so the same part and same PCB can be
used for all sorts of creative purposes.
/tvb
----- Original Message -----
From: "Randy Warner" Randy@synergy-gps.com
To: "Discussion of precise time and frequency measurement version=3.1.0"
time-nuts@febo.com
Sent: Tuesday, August 08, 2006 12:23
Subject: Re: [time-nuts] Frequency Dividers
Guys,
First off, what I am about to do is ask a REALLY STUPID question, but
more and more of the GPS stuff I do is drifting towards the precision
timing end of things, so I thought I should ask.
I have been seeing a lot of traffic concerning making 10MHz frequency
dividers using PIC's. While they provide an elegant solution to
providing an accurate 1PPS from a precision source, I have to ask if
there is a reason for going this route? I am just using three HCT40103
down counters hooked to a DS4000 to get what I think is a very stable
1PPS. Am I missing something? I realize 40103's are as old as dirt (I
guess I am showing my 4000 series CMOS days), but the HCT series have
plenty of bandwidth.
Please be gentle....
Randy
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Hi Randy,
For most purposes seven 7490's or four HC390's or
three HCT40103, etc. will work just fine. Speaking
for myself, the main thing was parts count. And being
more of a software person than hardware I prefer a
one IC solution (which has the fun of software) to
a 3, 4, or 7 IC solution.
The other issues, which may or may not have any
bearing on some applications is that the latency
and the tempco of a multi-chip solution is likely
worse than a single IC solution.
Lastly, once one has programmed a PIC you realize
that dividing by almost any number is just as easy
as 10M so the same part and same PCB can be
used for all sorts of creative purposes.
/tvb
Let me add this photo - I found in a box my first attempt
to make a PPS divider.
Let me add this photo - I found in a box my first attempt
to make a PPS divider as well as an early breadboard
prototype of the much simpler, PIC-based, divider.
http://www.leapsecond.com/pages/ppsdiv/ver1.jpg
/tvb
Randy Warner said the following on 08/08/2006 03:23 PM:
I have been seeing a lot of traffic concerning making 10MHz frequency
dividers using PIC's. While they provide an elegant solution to
providing an accurate 1PPS from a precision source, I have to ask if
there is a reason for going this route? I am just using three HCT40103
down counters hooked to a DS4000 to get what I think is a very stable
1PPS. Am I missing something? I realize 40103's are as old as dirt (I
guess I am showing my 4000 series CMOS days), but the HCT series have
plenty of bandwidth.
Hi Randy --
I think the concern in using the older discrete devices is their
potential for jitter in general, and temperature sensitivity on top of
that. But I've never done any experiments on just how big a problem
those issues are.
John
Tom,
Attached is my entry in the butt-ugly PPS divider contest. A whole lot
of 74HC192's and 74HC74's. I think this is circa 1999 or so.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Tom Van Baak
Sent: Tuesday, August 08, 2006 2:16 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency Dividers
Let me add this photo - I found in a box my first attempt to make a PPS
divider as well as an early breadboard prototype of the much simpler,
PIC-based, divider.
http://www.leapsecond.com/pages/ppsdiv/ver1.jpg
/tvb
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From: "Tom Van Baak" tvb@leapsecond.com
Subject: Re: [time-nuts] Frequency Dividers
Date: Tue, 8 Aug 2006 14:16:24 -0700
Message-ID: 001201c6bb2f$e85ffe60$1c15f204@computer
Let me add this photo - I found in a box my first attempt
to make a PPS divider as well as an early breadboard
prototype of the much simpler, PIC-based, divider.
However, I would not use any of them for any real work, since the MTBF of those
breadboards isn't longterm friendly. ;O)
A small CPLD such as XC9536 would also do it in one chip, you program in
friendly VHDL and know it will do the right thing. ;O)
Cheers,
Magnus
John,
I totally understand the concerns about stability. In the experiments I
have run the jitter is down in the ps range. Temp would be a whole other
animal. I have just been running these in the lab. Oh well, it's all
fun.
Randy
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of John Ackermann N8UR
Sent: Tuesday, August 08, 2006 2:31 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency Dividers
Randy Warner said the following on 08/08/2006 03:23 PM:
I have been seeing a lot of traffic concerning making 10MHz frequency
dividers using PIC's. While they provide an elegant solution to
providing an accurate 1PPS from a precision source, I have to ask if
there is a reason for going this route? I am just using three HCT40103
down counters hooked to a DS4000 to get what I think is a very stable
1PPS. Am I missing something? I realize 40103's are as old as dirt (I
guess I am showing my 4000 series CMOS days), but the HCT series have
plenty of bandwidth.
Hi Randy --
I think the concern in using the older discrete devices is their
potential for jitter in general, and temperature sensitivity on top of
that. But I've never done any experiments on just how big a problem
those issues are.
John
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Guys,
Sorry to post again, but it just dawned on me that I meant to post some
info concerning M12+, M12, GT, UT+, and probably even VP receivers. This
issue is one of the reasons the M12M is late coming out of the chute. If
I have posted this before I apologize. Just too many things rattling
around in my brain.
CRITICAL: Whenever you run a Self-Test on any of these receivers, MAKE
ABSOLUTELY SURE that you wait until you have gotten the response message
before you issue any additional commands. If you get REALLY lucky and
send your command at EXACTLY the wrong time while the UART is in limbo
you can get stuck in a lovely "do...while" loop that can only be exited
by cycling power to the receiver. A clue that this has occurred is that
the 1PPS also stops. The Self-Test code in the M12M has been changed to
keep this from happening.
Looking back, this explains a lot of the unexplained random failures in
cell towers reported over the years by a couple of the carriers.
Absolutely unrepeatable. Almost impossible to troubleshoot. We just
found it by accident.
Now, before any of you wise guys try to repeat this problem, bear in
mind that statistically it seems to happen maybe once per 200,000 Self
Tests.
Randy
Well, since I am not versed in anything but Fortran or Basic, I would have
to go the old fashioned way. - Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Randy Warner
Sent: Tuesday, August 08, 2006 5:38 PM
To: Tom Van Baak; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Ugly Frequency Dividers
Tom,
Attached is my entry in the butt-ugly PPS divider contest. A whole lot
of 74HC192's and 74HC74's. I think this is circa 1999 or so.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Tom Van Baak
Sent: Tuesday, August 08, 2006 2:16 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency Dividers
Let me add this photo - I found in a box my first attempt to make a PPS
divider as well as an early breadboard prototype of the much simpler,
PIC-based, divider.
http://www.leapsecond.com/pages/ppsdiv/ver1.jpg
/tvb
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That remembers me the ugliest (or most exotic?)
frequency divider i ever saw:
It was part of a Marconi (damn, i don't remember the
model number, but it was an OOOOOLD model), more
precisely the 600 MHz divide by ten prescaler.
The input divider was based on two tunnel diodes that
acted as a div. by two divider followed by the really
most bizarre divide by five unit i ever saw: Fifteen
discrete NPN transistors arranged in a star (or
pentagon (Helloooo Echelon!! ) ) topology with the
input placed at the center of the star. The 15
transistor were in a symmetrical loop of 5 three
transistor units working in a closed loop.
Years later, i've made searches to find the schematic
of this prescaler, but without the model number, this
is quasi-impossible.
If one of this forum's members has this schematic, i
would be pleased to ask for a copy!
Damn! That strange "star" all-transistor divider could
count up to 300 MHz after all!!!
Have a good day gang and keep this forum running!!
73 de Normand Martel VE2UM
Montreal, Quebec, Canada
--- Randy Warner Randy@synergy-gps.com wrote:
Tom,
Attached is my entry in the butt-ugly PPS divider
contest. A whole lot
of 74HC192's and 74HC74's. I think this is circa
1999 or so.
-----Original Message-----
From: time-nuts-bounces@febo.com
[mailto:time-nuts-bounces@febo.com] On
Behalf Of Tom Van Baak
Sent: Tuesday, August 08, 2006 2:16 PM
To: Discussion of precise time and frequency
measurement
Subject: Re: [time-nuts] Frequency Dividers
Let me add this photo - I found in a box my first
attempt to make a PPS
divider as well as an early breadboard prototype of
the much simpler,
PIC-based, divider.
http://www.leapsecond.com/pages/ppsdiv/ver1.jpg
/tvb
time-nuts mailing list
time-nuts@febo.com
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