taken from:
http://digital.ni.com/public.nsf/allkb/1EE0DD8AF67922FA86256F720071DECF
The null modem cable is frequently called a crossover cable. It is used to allow two serial Data Terminal Equipment (DTE) devices to communicate with each other without using a modem or a Data Communications Equipment (DCE) device in between. For this to happen, the Transmit (TXD) pin of one device needs to be connected to the Receive (RXD) pin of the other device. To enable handshaking between the two devices, the Request to Send (RTS) pin of one device must be connected to the Clear to Send (CTS) pin of the other device. Because these pins are "crossed" on the two cable terminals, the name crossover cable is used.
A straight-through cable is used to connect a DTE device to a DCE device. The TXD-RXD and RTS-CTS pins are not cross-connected in this case, hence the term straight through cable.
The built-in serial port on a PC is a DTE device. Modems and printers are examples of DCE devices. Note that an instrument with serial interface could be either a DTE or a DCE device. It is best to check the user manual of the instrument to find out the device type. For more information regarding DTE and DCE devices, please see the links below.
To tell if your cable is null modem or straight though, you can search the part number at ni.com, the product description will tell if it is null modem. Alternatively you can use a hand held DMM to test continuity on the individual pins of your serial cable. If every pin is electrically connected to the corresponding pin on the other end, i.e.: pin 1 to pin1, pin 2 to pin 2, etc. then the cable is straight through.
19 April 2011
02 April 2011
20 Excel Formula
http://www.databison.com/index.php/20-useful-excel-formulas-you-must-know/
DATEVALUE = Converts a date in the form of text to a serial number
DAY = Converts a serial number to a day of the month
MONTH = Converts a serial number to a month
YEAR = Converts a serial number to a year
LEFT = Returns the leftmost characters from a text value
LEN = Returns the number of characters in a text string
RIGHT = Returns the rightmost characters from a text value
AVERAGE = Returns the average of its arguments
COUNT = Counts how many numbers are in the list of arguments
COUNTIF = Counts the number of nonblank cells within a range that meet the given criteria
MAX = Returns the maximum value in a list of arguments
AND = Returns TRUE if all its arguments are TRUE
IF = Specifies a logical test to perform
ROUNDDOWN = Rounds a number down, toward zero
ROUNDUP = Rounds a number up, away from zero
SUM = Adds its arguments
SUMIF = Adds the cells specified by a given criteria
OFFSET = Returns a reference offset from a given reference
VLOOKUP = Looks in the first column of an array and moves across the row to return the value of a cell
ISERROR = Returns TRUE if the value is any error value
DATEVALUE = Converts a date in the form of text to a serial number
DAY = Converts a serial number to a day of the month
MONTH = Converts a serial number to a month
YEAR = Converts a serial number to a year
LEFT = Returns the leftmost characters from a text value
LEN = Returns the number of characters in a text string
RIGHT = Returns the rightmost characters from a text value
AVERAGE = Returns the average of its arguments
COUNT = Counts how many numbers are in the list of arguments
COUNTIF = Counts the number of nonblank cells within a range that meet the given criteria
MAX = Returns the maximum value in a list of arguments
AND = Returns TRUE if all its arguments are TRUE
IF = Specifies a logical test to perform
ROUNDDOWN = Rounds a number down, toward zero
ROUNDUP = Rounds a number up, away from zero
SUM = Adds its arguments
SUMIF = Adds the cells specified by a given criteria
OFFSET = Returns a reference offset from a given reference
VLOOKUP = Looks in the first column of an array and moves across the row to return the value of a cell
ISERROR = Returns TRUE if the value is any error value
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