Unused BS2 pins question...
Archiver
Posts: 46,084
My current project only requires that I use 4 pins on the BS2 as
inputs. These pins are connected to 10K pull-ups, but my question is
should the other unused pins be pulled up also, or is it better to
pull them down to ground? Is there a difference in current
consumption of the BS2, whether unused pins are tied 'high' or 'low'?
Thank you....
Jim D. Martin
inputs. These pins are connected to 10K pull-ups, but my question is
should the other unused pins be pulled up also, or is it better to
pull them down to ground? Is there a difference in current
consumption of the BS2, whether unused pins are tied 'high' or 'low'?
Thank you....
Jim D. Martin
Comments
lots of sense on TTL logic, where a floating,
unused input makes a really good noise-coupler
into your circuitry and other logic.
On the BS2, you're talking about the input
to a PIC chip. As long as your code ignores
the input values, the chip will also. This
means there won't be any current flow on
a 'floating' pin to worry about, so you
don't need to tie them anywhere.
Note the data pins on the PIC have various
protection diodes on them internally, which
also helps cut down on coupled noise into
the circuit.
--- In basicstamps@yahoogroups.com, "Jim D. Martin" <fw_econo@y...>
wrote:
> My current project only requires that I use 4 pins on the BS2 as
> inputs. These pins are connected to 10K pull-ups, but my question
is
> should the other unused pins be pulled up also, or is it better to
> pull them down to ground? Is there a difference in current
> consumption of the BS2, whether unused pins are tied 'high'
or 'low'?
>
> Thank you....
>
> Jim D. Martin
>inputs. These pins are connected to 10K pull-ups, but my question is
>should the other unused pins be pulled up also, or is it better to
>pull them down to ground? Is there a difference in current
>consumption of the BS2, whether unused pins are tied 'high' or 'low'?
>
>Thank you....
>
>Jim D. Martin
Tie unused pins either high or low, it does not matter which, or have
your program set them as outputs, either high or low. The trouble
with floating inputs is that they will can float to intermediate
levels that make the input buffers draw useless power supply current.
I don't think it ever gets to a level that hurts the Stamp itself,
but it is a big concern if you are trying to conserve battery life.
By pulling the pins up or down or by making them outputs, the input
buffer is brought to a definite level that does not draw power supply
current.
-- Tracy
> Tie unused pins either high or low, it does not matter which
My only concern with this advice is that as the stamp pins are
*programmable*, you run the risk of a software mistake causing a hardware
failure (i.e. letting out the "magic blue smoke" [noparse]:)[/noparse]
If, for example, you tie all the unused pins to ground, then
inadvertently update the software where it toggles those pins to a
output/hi state, you would have a dead short that could damage/destroy
the chip. (remember Murphy watches for just this type of environment to
exploit! [noparse]:)[/noparse]
I suggest that if you're concerned about the state of the pins (power
draw, static electricity issues, erratic state, etc.) you could use pull
up resistors so a software problem wouldn't cause a direct short in a
worst case scenario... [noparse]:)[/noparse]
Vern
--
Vern Graner CNE/CNA/SSE | "If the network is down, then you're
Senior Systems Engineer | obviously incompetent so why are we
Texas Information Services | paying you? Of course, if the network
vern@t... www.txis.com | is up, then we obviously don't need
Cell 507-7851 Desk 328-8947 | you, so why are we paying you?" VLG
Tracy Allen said:
>>My current project only requires that I use 4 pins on the BS2 as
>>inputs. These pins are connected to 10K pull-ups, but my question is
>>should the other unused pins be pulled up also, or is it better to
>>pull them down to ground? Is there a difference in current
>>consumption of the BS2, whether unused pins are tied 'high' or 'low'?
>>
>>Thank you....
>>
>>Jim D. Martin
>
> Tie unused pins either high or low, it does not matter which, or have
> your program set them as outputs, either high or low. The trouble
> with floating inputs is that they will can float to intermediate
> levels that make the input buffers draw useless power supply current.
> I don't think it ever gets to a level that hurts the Stamp itself,
> but it is a big concern if you are trying to conserve battery life.
> By pulling the pins up or down or by making them outputs, the input
> buffer is brought to a definite level that does not draw power supply
> current.
>
> -- Tracy
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
or low *through a pullup or pulldown resistor of ~1k*, or make them
outputs, either high or low.". Making them outputs does not take
any hardware (the resistor), but it does take a program instruction.
Using the pullup/down resistor does not require at PBASIC
instruction, because the pins are all inputs by default after the
reset.
-- Tracy
>Tracy Allen said:
>> Tie unused pins either high or low, it does not matter which
>
>My only concern with this advice is that as the stamp pins are
>*programmable*, you run the risk of a software mistake causing a hardware
>failure (i.e. letting out the "magic blue smoke" [noparse]:)[/noparse]
>
>If, for example, you tie all the unused pins to ground, then
>inadvertently update the software where it toggles those pins to a
>output/hi state, you would have a dead short that could damage/destroy
>the chip. (remember Murphy watches for just this type of environment to
>exploit! [noparse]:)[/noparse]
>
>I suggest that if you're concerned about the state of the pins (power
>draw, static electricity issues, erratic state, etc.) you could use pull
>up resistors so a software problem wouldn't cause a direct short in a
>worst case scenario... [noparse]:)[/noparse]
>
>Vern
>
>--
>Vern Graner CNE/CNA/SSE | "If the network is down, then you're
>Senior Systems Engineer | obviously incompetent so why are we
>Texas Information Services | paying you? Of course, if the network
>vern@t... www.txis.com | is up, then we obviously don't need
>Cell 507-7851 Desk 328-8947 | you, so why are we paying you?" VLG
>
>
>
>Tracy Allen said:
>>>My current project only requires that I use 4 pins on the BS2 as
>>>inputs. These pins are connected to 10K pull-ups, but my question is
>>>should the other unused pins be pulled up also, or is it better to
>>>pull them down to ground? Is there a difference in current
>>>consumption of the BS2, whether unused pins are tied 'high' or 'low'?
>>>
>>>Thank you....
>>>
>>>Jim D. Martin
>>
>> Tie unused pins either high or low, it does not matter which, or have
>> your program set them as outputs, either high or low. The trouble
>> with floating inputs is that they will can float to intermediate
>> levels that make the input buffers draw useless power supply current.
>> I don't think it ever gets to a level that hurts the Stamp itself,
>> but it is a big concern if you are trying to conserve battery life.
>> By pulling the pins up or down or by making them outputs, the input
>> buffer is brought to a definite level that does not draw power supply
>> current.
>>
>> -- Tracy
>>
>>
>>
>> To UNSUBSCRIBE, just send mail to:
>> basicstamps-unsubscribe@yahoogroups.com
>> from the same email address that you subscribed. Text in the Subject and
>> Body of the message will be ignored.
>>
>>
>> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>>
>>
>>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the
>Subject and Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
This is a very good question. If you want to ensure that the BASIC
Stamp consumes as little current as possible, make sure all unused I/O
pins are:
1) Set to inputs (default) and externally tied high or low
or
2) Set to output high or low but not electrically connected to
anything.
It doesn't matter in either case whether or not they are tied or driven
high or low (both states produce the same current consumption.
If, on the other hand, they are set to inputs and left floating (not
electrically connected high or low) they will cause the interpreter chip
to consume current erratically (in a non-deterministic fashion).
--Jeff Martin
Engineering Manager
Parallax, Inc.
>
Original Message
> From: Jim D. Martin [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=aWuz-_9GcRj7gjhwgHFqhraX9E_czLhZMyPWpajK6eUWN3JjXKbz5TAFbp-fD0x7LdX0wqg0OPRbjrTl]fw_econo@y...[/url
> Sent: Tuesday, July 22, 2003 7:56 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Unused BS2 pins question...
>
>
> My current project only requires that I use 4 pins on the BS2 as
> inputs. These pins are connected to 10K pull-ups, but my question is
> should the other unused pins be pulled up also, or is it better to
> pull them down to ground? Is there a difference in current
> consumption of the BS2, whether unused pins are tied 'high' or 'low'?
>
> Thank you....
>
> Jim D. Martin
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
This message has been scanned by WebShield. Please report SPAM to
abuse@p....