SHIFTIN POST mode
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Posts: 46,084
Group,
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be sure.
Thank you.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be sure.
Thank you.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
18 microseconds after the falling clock edge.
Can you confirm if 18 microseconds is correct?
Ken
====================================
In a message dated 7/19/2004 6:54:41 AM Pacific Standard Time,
jwilliams@p... writes:
The point is that the data line is sampled AFTER the clock when using
POST modes. Is there something more to your question?
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=SnW1ODyjHbTl5FbeDFcvOknbwRzRhvESjdAHpG9PL_FBa1h_g9b7Een5kOuOxotfvIR37zL0Y-SP2Ho]smartdim@a...[/url
Sent: Sunday, July 18, 2004 9:45 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Group,
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro
seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be
sure.
Thank you.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
POST modes. Is there something more to your question?
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=xFMl2p1GWm-OJfFBlVdYJOnrJ2mseieaV7EJv-jiJcZsWYreY7JfMmTyzo1trlXWkHoED186]smartdim@a...[/url
Sent: Sunday, July 18, 2004 9:45 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Group,
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro
seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be
sure.
Thank you.
Ken
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=tm9EJida3DKoY4HKBlRt7ZkXW1rGgbzqCT7v2edyxYR1UpeInXhyGPJ-QC2GgFT7qUwgrFOm4SfD]smartdim@a...[/url
Sent: Monday, July 19, 2004 9:10 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Yes there is more to my question. The help file indicates the post
sample is
18 microseconds after the falling clock edge.
Can you confirm if 18 microseconds is correct?
Ken
====================================
In a message dated 7/19/2004 6:54:41 AM Pacific Standard Time,
jwilliams@p... writes:
The point is that the data line is sampled AFTER the clock when using
POST modes. Is there something more to your question?
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=tm9EJida3DKoY4HKBlRt7ZkXW1rGgbzqCT7v2edyxYR1UpeInXhyGPJ-QC2GgFT7qUwgrFOm4SfD]smartdim@a...[/url
Sent: Sunday, July 18, 2004 9:45 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Group,
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro
seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be
sure.
Thank you.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
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I think the timing diagram is _not_ referring to the time between the
falling edge of the clock and the sample. "Th" is the time the
clock is high, and "Tl" is the time the clock is low. The 18
microsecond figure for the BS2SX refers to the time low, 18
microseconds low, 5.6 microseconds high. Add those up and take the
inverse and you get the SERIN transmission rate of ~42 kbits per
second. Other stamps differ. For example, the BS2 is 14us/46us/16.7
kbps.
It appears from the diagram and from common sense that the sample is
taken shortly before the rising edge of the clock pulse, in order to
allow lots of time for the data to settle after each clock pulse. But
the exact time is not documented as far as I can tell. Is this is
something really critical for you to know?
-- Tracy
>
>
>Yes there is more to my question. The help file indicates the post sample is
>18 microseconds after the falling clock edge.
>
>Can you confirm if 18 microseconds is correct?
>
>Ken
>====================================
>
>
>In a message dated 7/19/2004 6:54:41 AM Pacific Standard Time,
>jwilliams@p... writes:
>
>The point is that the data line is sampled AFTER the clock when using
>POST modes. Is there something more to your question?
>
>-- Jon Williams
>-- Applications Engineer, Parallax
>-- Dallas Office
>
>
>
Original Message
>From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=P-S4K6FMUJXvhflrADsSMs2XGDn75-_mf2g1U8esYIcBBXOxJbzUzPuE4UKVi42A4hsFXCIn]smartdim@a...[/url
>Sent: Sunday, July 18, 2004 9:45 PM
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
>
>
>Group,
>
>Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
>confirm I correctly interpret the help file information.
>
>Using a BS2p and POST mode, data is read into the variable 18 micro
>seconds
>after the clock falling edge.
>
>The help file seems straight forward in this area, but I want to be
>sure.
>
>Thank you.
>
>Ken
of the sample is not critical.
The reason I was asking is that I am using shiftin in an
unconventional manner, where the data to be sampled is not availble
for about 4 microseconds after the falling edge of the clock.
Emperical experimentation tells me I am not losing any bits, but I
would feel more comfortable knowing there was some margin....
For example, if my data is not valid until 4 microseconds after the
falling edge, and the sample is taken 5 microseconds after the
falling edge, that would cause me some concern.
I suppose if I could set up a test that determines the sample time by
presenting data at 1 microsecond intervals going backwards from 18
microseconds to see at about what point the data is not read into my
variable.
ken
--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> Hi Ken,
>
> I think the timing diagram is _not_ referring to the time between
the
> falling edge of the clock and the sample. "Th" is the time the
> clock is high, and "Tl" is the time the clock is low. The 18
> microsecond figure for the BS2SX refers to the time low, 18
> microseconds low, 5.6 microseconds high. Add those up and take the
> inverse and you get the SERIN transmission rate of ~42 kbits per
> second. Other stamps differ. For example, the BS2 is
14us/46us/16.7
> kbps.
>
> It appears from the diagram and from common sense that the sample
is
> taken shortly before the rising edge of the clock pulse, in order
to
> allow lots of time for the data to settle after each clock pulse.
But
> the exact time is not documented as far as I can tell. Is this is
> something really critical for you to know?
>
> -- Tracy
>
>
> >
> >
> >Yes there is more to my question. The help file indicates the post
sample is
> >18 microseconds after the falling clock edge.
> >
> >Can you confirm if 18 microseconds is correct?
> >
> >Ken
> >====================================
> >
> >
> >In a message dated 7/19/2004 6:54:41 AM Pacific Standard Time,
> >jwilliams@p... writes:
> >
> >The point is that the data line is sampled AFTER the clock when
using
> >POST modes. Is there something more to your question?
> >
> >-- Jon Williams
> >-- Applications Engineer, Parallax
> >-- Dallas Office
> >
> >
> >
Original Message
> >From: smartdim@a... [noparse][[/noparse]mailto:smartdim@a...]
> >Sent: Sunday, July 18, 2004 9:45 PM
> >To: basicstamps@yahoogroups.com
> >Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
> >
> >
> >Group,
> >
> >Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I
want to
> >confirm I correctly interpret the help file information.
> >
> >Using a BS2p and POST mode, data is read into the variable 18
micro
> >seconds
> >after the clock falling edge.
> >
> >The help file seems straight forward in this area, but I want to
be
> >sure.
> >
> >Thank you.
> >
> >Ken
The help file (and the printed manual) are really indicating the typical
width of the clock pulse (high) and clock pulse (low), which in the case
of the BS2p is 5.6 us and 18 us, respectively. The critical thing to
understand is that the data line is sampled for the first time
immediately before the 2nd clock pulse is generated (thus being as far
after the first clock pulse as possible) when the "POST" mode is used.
The actual time at which it samples has not been tested, but rather the
high and low pulse generated on the clock is easily tested by measuring
it with an oscilloscope.
The more accurate way to say what you're asking is: The data line is
sampled less than 18 us after the clock line goes low.
Remember, the timing of any part of the BASIC Stamp (and most electronic
equipment) is always susceptible to variances caused by temperature,
humidity, voltage and the initial accuracy of the components. If your
application is reaching a critical threshold, you should measure the
clock pulse generated by your BS2p's SHIFTIN command on an oscilloscope
while the module is in the exact circuit and environment you intend for
it to function in.
One other note: Most devices that are slaves on the SPI buss are
hardware state-machines, rather than microcontrollers, so it is quite
typical that their response time to a rising or falling edge of the
clock will be much quicker than 18 us. Also, if the slave device
responds to the rising edge of the clock, you're even better off because
it now has just less than 23.6 us to stabilize the data line (the T0 +
T1 time).
--Jeff Martin
Parallax, Inc.
Web: http://www.parallax.com
Original Message
From: Jon Williams
Sent: Monday, July 19, 2004 7:58 AM
To: 'basicstamps@yahoogroups.com'
Subject: RE: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
I'll have to check with engineering -- it varies by BASIC Stamp module.
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ym5eVlYEwGeRl9HFSv4QDwzMVHxrTez7uGskdyefiKIX6MSD49SGWTxtoFrzexmmoNdwfEzx_w]smartdim@a...[/url
Sent: Monday, July 19, 2004 9:10 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Yes there is more to my question. The help file indicates the post
sample is
18 microseconds after the falling clock edge.
Can you confirm if 18 microseconds is correct?
Ken
====================================
In a message dated 7/19/2004 6:54:41 AM Pacific Standard Time,
jwilliams@p... writes:
The point is that the data line is sampled AFTER the clock when using
POST modes. Is there something more to your question?
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ym5eVlYEwGeRl9HFSv4QDwzMVHxrTez7uGskdyefiKIX6MSD49SGWTxtoFrzexmmoNdwfEzx_w]smartdim@a...[/url
Sent: Sunday, July 18, 2004 9:45 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] SHIFTIN POST mode
Group,
Regarding SHIFTIN using MSBPOST (or LSBPOST for that matter) I want to
confirm I correctly interpret the help file information.
Using a BS2p and POST mode, data is read into the variable 18 micro
seconds
after the clock falling edge.
The help file seems straight forward in this area, but I want to be
sure.
Thank you.
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
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