Hi, The following is technical, but I'm sure many would find this useful: A parity bit is used to provide error detection possible during serial communication. This is done by counting number of binary 1's in a given seven bit data. As you may have seen, there are two versions: odd parity and even parity, with the parity bit set to 1 if the total number of 1's in a seven bit data stream is not odd (for odd parity) and not even (for even parity). To explain this further, you need to understand that, for computers and computerized equipment, all they know is binary system - bunch of 0's and 1's. All they know is to perform some things based on a given binary pattern. For modern notetakers, the processor can work with 32 bits at a time, with desktops working with 64 binary numbers at a time. The binary pattern may represent one of two things: data and program machine code or instructions. Even communication channels use binary to send and receive data, hence the need to make sure that data is intact. This is where so-called "error detection" routine comes in to make sure that whatever data you send from one computer is the same one the other person will get on another computer. Do not confuse this with ECC "error correcting code", as ECC is used when trying to correct errors when sending and receiving data, including querying possibly corrupted data on a disk. Now back to parity bit: ASCII serial transmission uses eight bits to transfer data, which is enough to code letters, symbols and other useful info (the actual serial link sends and receives one bit at a time). To make sure that each binary data stream is intact, we use a bit to denote number of 1's found in a data stream. For example, if we set parity bit to odd and wish to transfer a space character (binary: 00100000). The transmitter will see that there is only a single 1 (odd number), so it'll set the parity bit (usually the right-most bit) to 0. On the other hand, if we wish to transmit capital A (binary: 01000001), the transmitter will see that there are two 1's (even number), thereby setting the parity bit to 1 to make the whole string contain odd number of 1's. If we translate these two examples to even parity setting, the result will be opposite of what we've seen: on a space character, the parity bit will be set to 1 so we can have two 1's in the string; for capital A, the parity bit will be set to 0 since it already contains even number of 1's. As for connection with printers: this is not a printer file setting; this is a communication link setting, so any serial printer would obey the parity rule set by users - usually it is even parity. Hope this explains the original question. Cheers, Joseph -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Tyler Sent: Wednesday, July 11, 2012 3:27 PM To: [email protected] Subject: [Braillenote] odd and even parity
Hello! Explain the odd and even parity thing. Does it have to do with printing and serial ports or what? Tyler Z ___ Replies to this message will go directly to the sender. If your reply would be useful to the list, please send a copy to the list as well. To leave the BrailleNote list, send a blank message to [email protected] To view the list archives or change your preferences, visit http://list.humanware.com/mailman/listinfo/braillenote
