pull up register for???

[nirav]

what is the use of pull up register,i got the idea of pull down register from this site only but here instead of using the ground we have to use vdd (supply)?and yes then what happen when switch is on??please discuss

[jwax]

A pull-up resistor simply holds a node at Vcc. (High)
When it's desired to toggle the pin low, a ground (or Vdd)is put on the pin to take it low.

[philba]

resistor, not register.<p>Pull up vs pull down. They do basically the same task - to prevent noise from effecting an input pin. Pull-ups are more traditional since TTL drew less current when pulled high and you can wire-or multiple devices on a given pin (i.e., a bus although tri-stating is a better way). <p>You will see the term open-collector output for a lot of parts - this means you should use a pull up (or perhaps a pull down) resistor on the output. Check the given device's data sheet. <p>A simple example - using a switch with digital logic (or a microcontroller).
<p>Phil<p>[ April 17, 2005: Message edited by: philba ]</p>

[nirav]

hi,
thanks for giving the explanation,i got the idea,but here in my case i am using bidirectional data line ,so for input and output i am using the same microcontroller pin,so when i will configure controller pin as a output pin, then how will it( pull up registor)works<p> it makes any diffrence??..<p>nirav
<p>
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:
resistor, not register.<p>Pull up vs pull down. They do basically the same task - to prevent noise from effecting an input pin. Pull-ups are more traditional since TTL drew less current when pulled high and you can wire-or multiple devices on a given pin (i.e., a bus although tri-stating is a better way). <p>You will see the term open-collector output for a lot of parts - this means you should use a pull up (or perhaps a pull down) resistor on the output. Check the given device's data sheet. <p>A simple example - using a switch with digital logic (or a microcontroller).
<p>Phil<p>[ April 17, 2005: Message edited by: philba ]<hr></blockquote>

[philba]

resistor not register. note the spelling. you won't get what you want if you ask for a register.<p>It completely depends on what is conected to the pin and what kind of protocol. I2C? SPI? basically, I can't answer your question with out knowing that information.

[nirav]

sorry ,for that really,it is a registor,
this pin is connected to one sensor which is measure humidity and temperature(humidity and temperature sensor),and i have to make a protocol ,which is already given in the data sheet of this sensor,I am using sht1x/sht7x humidity and temperature sensor(company-sensirion)and i am using pic 12f675 microcontroller.so please discusss<p>thanks<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:
resistor not register. note the spelling. you won't get what you want if you ask for a register.<p>It completely depends on what is conected to the pin and what kind of protocol. I2C? SPI? basically, I can't answer your question with out knowing that information.<hr></blockquote>

[philba]

sheesh. just use the circuit from the datasheet and call it anything you want. But I've never heard of a pull-up registor (or register) and the data sheet says "pull-up resistor". It also says 10K.<p>The protocol is not I2C but looks similar. Why oh why do companies come up with random protocols when I2C and SPI are well understood and supported. You'll have to bit bang it on the 675. good luck.<p>By the way, at this point I have no idea what you are asking.<p>Phil

[nirav]

i think u have already read the datasheets for senssor and pic controller,<p>what i understood:
if u will see the protocol, after sending the command sensor will pull down the data line as acknowledgement.so it will be done with the help of pull up registor ,to pull the data line down sensor must switch close so pin will be connected to gnd and dataline goes down ,and when sensor wants to give data line high it will simply open the switch so pin got vcc through 10k. Am i right???<p>so my question is how pull up registor will work when i will configure the same pin as output.
means what should be the function of pull up registor at this time..<p>thnaks for discussing
nirav<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:
sheesh. just use the circuit from the datasheet and call it anything you want. But I've never heard of a pull-up registor (or register) and the data sheet says "pull-up resistor". It also says 10K.<p>The protocol is not I2C but looks similar. Why oh why do companies come up with random protocols when I2C and SPI are well understood and supported. You'll have to bit bang it on the 675. good luck.<p>By the way, at this point I have no idea what you are asking.<p>Phil<hr></blockquote>

[nirav]

pull up resistor,not register or registor<p> <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by nirav:
i think u have already read the datasheets for senssor and pic controller,<p>what i understood:
if u will see the protocol, after sending the command sensor will pull down the data line as acknowledgement.so it will be done with the help of pull up registor ,to pull the data line down sensor must switch close so pin will be connected to gnd and dataline goes down ,and when sensor wants to give data line high it will simply open the switch so pin got vcc through 10k. Am i right???<p>so my question is how pull up registor will work when i will configure the same pin as output.
means what should be the function of pull up registor at this time..<p>thnaks for discussing
nirav<p> <hr></blockquote>

[sofaspud]

I don't want to get in the middle of this, but the pull-up resistor will function the same way whether the data line is I, O, or I/O.
When the negative side of the pull up resistor is a short or low impedance to ground, that point will be at 0V. When the negative side of the resistor is an open or high impedance to ground, that point will be at Vcc.

[philba]

Yup. In simple words, just use the circuit from the datasheet and it will work fine. <p>In slightly more detail, when the pin is output from the 675, the PIC is driving it, when its input, the sensor is (er, should be) driving it. Pull up doesn't care what is driving it.<p>Your bigger task is the comm protocol. Not that hard to do but you'll need to be careful with the timing and sequencing of the data & clock lines. Look around the sensiron site for programming examples. <p>Phil

[nirav]

thanks ,i got the idea,
only last little question,
in my sensirion datasheet in 2.2.2 column i read that
"to avoid signal contention the microcontroller should only drive DATA low "
what does this mean????
i have to check somthin (port characteristics)in my pic 12f675 datasheet for that???<p>
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:
Yup. In simple words, just use the circuit from the datasheet and it will work fine. <p>In slightly more detail, when the pin is output from the 675, the PIC is driving it, when its input, the sensor is (er, should be) driving it. Pull up doesn't care what is driving it.<p>Your bigger task is the comm protocol. Not that hard to do but you'll need to be careful with the timing and sequencing of the data & clock lines. Look around the sensiron site for programming examples. <p>Phil<hr></blockquote>

[rshayes]

There are at least two ways of implementing bidirectional signal flow on a wire.<p>The oldest was referred to as Wired-OR. Here a data line had one pullup resistor, with the data line going to several locations. Each location connected to the line with the collector of a transistor whose emitter was grounded. If any transistor was turned on, the line would be pulled down to ground. If two transistors were accidently turned on at the same time, the data would be corrrupted, but no physical damage would result. This method is simple, but does not work well at high speeds, since the single pullup resistor has to charge all of the stray capacitance associated with the data line and the connected transistors.<p>A more complex method uses a line with no pullup resistor, but the drive circuits at each location have three states. When transmitting data, a driver either sources current to force the line positive or sinks current to force the line to ground. All of the other drivers are placed in a high impedance state, and can neither source or sink current.<p>This type of connection is faster, but the drivers are much more complicated than a single transistor and are usually implemented as an integrated circuit. If two drivers are turned on at the same time, and one is sourceing current with the other sinking current, it is possible to damage the driver circuits.<p>This is what is referred to as "signal contention". Basically two devices are trying to put opposite signals on the same wire at the same time.<p>Many devices use programmable I/O ports. Initially, these are placed in an input mode with a high input impedance. If the pin is pulled high or low by an external device, no damage will occur. Later, some of these ports will be redefined as output ports. After a port is defined as an output purt, it can be damaged by contention with another signal on the line or by a short circuit to either ground or the supply potential. It is the responsibility of the programmer to see that this doesn't happen.<p>It appears that the device that you are using is arranged to use the old Wired-OR method to insure that damage will not occur even if the programmer makes a mistake and enables two ports as output ports on the same line.

[philba]

Have you looked at the code examples? they are pretty clear about what you have to do. I'd just use the data sheet diagram and crib the example code (not lose any sleep about it).

[John Brown]

Somebody may have mentioned this already, I can't be bothered to wade through all the posts, but...
On certain microcontrollers there is a pull-up REGISTER which is used to enable or disable built-in pull-ups on a pin-by-pin basis. They're not usually resistors, they're FETs which source a fairly low current (about 50 uA if I remember correctly)