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RS-232 is a standard for serial data communication between a DTE (Data Terminal Equipment) and a DCE (Data communication Equipment). This originally meant a dumb terminal and a modem; it was only later that personal computers, printers, and other devices started to make use of the standard. |
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RS-232 is a standard for [serial data communication]? between a DTE ([Data Terminal Equipment]?) and a DCE ([Data communication Equipment]?). This originally meant a dumb terminal and a modem; it was only later that personal computers, printers, and other devices started to make use of the standard. |
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RS-232 serial connections on PCs are gradually being replaced by USB which is faster and has simpler (to connect/configure, but more difficult to build) connectors. |
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RS-232 serial connections on PCs are gradually being superseded by USB which is faster and has connectors that are simpler to connect and use; overall USB equipment is more difficult to build and therefore more expensive. |
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Using asynchronous communication, characters are send one by one, commonly each character is marked by a single start bit, seven or eight data bits, possibly a "parity" bit, and a stop bit. The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels, the standard transmission speeds and connector types. |
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Using asynchronous communication, characters are send one by one, commonly each character is marked by a single start bit, seven or eight data bits, possibly a "parity" bit, and a stop bit. The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels, the standard transmission speeds and connector types. |
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Typical RS-232 devices include external modems; some printers (most modern printers are parallel, USB, or network); device communications or statistics ports (for example, PBX SMDR or router configuration). |
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Typical RS-232 devices include external modems; some printers (most modern printers are parallel, USB, or network); device communications or statistics ports (for example, PBX SMDR or router configuration). |
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Originally the standard specified 25-pin "DB" connectors. Most of these pins were unused by many devices, however, so it was common for machines to save money by using smaller connectors. The IBM PC was released with 9-pin serial connectors, and that became the de facto standard of today for PCs; most host devices still use 25-pin connectors. Male and female connectors are used--often cable ends are male and device connectors are female; but not always; m-m and f-f "gender changers" are available. |
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The standard specifies 25 different signal connections and a 25-pin "DB" connector was commonly used. Most of these pins were unused by many devices, however, so it was common for machines to save money by using smaller connectors. The IBM PC was released with 9-pin serial connectors, and that became the de facto standard of today for PCs; most host devices still use 25-pin connectors. Male and female connectors are used--often cable ends are male and device connectors are female; but not always; m-m and f-f "gender changers" are available. |
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Software-wise there are a multitude of settings for serial connections. Most common settings are speed and parity. |
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Software-wise there are a multitude of settings for serial connections. Most common settings are speed, parity, and stop bits. |
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Parity is a method of verifying accuracy of data. It defines "parity bits" in each block of data as follows: data b/parity/parity bits. The most common setting is 8/none/1 which would indicate 8 bits of data, no parity checking, one parity bit. Data bits are normally 7 or 8; parity may be none, even, odd, mark, space, or several others, parity bit may be 0, 1, or 2. |
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Parity is a method of verifying accuracy of data. Parity is either none (not used), odd, or even. Parity works by modifying the data in each byte sent (or restricting the bytes sent if you like). Parity none is simple, the data is not changed. In even parity the data is arranged so that the number of 1 bits (that is, the total count of them in a binary byte) is an even number; this is arranged by setting the parity bit (usually the most significant bit) to be a 0 or 1 accordingly. In odd parity the number of 1 bits is an odd number. Parity can be used by the receiver to detect transmission errors - if a byte is received with the wrong number of 1 bits, then it must have been corrupted. |
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Other settings define when pins will send handshake signals, or other data integrity checks. The most common of these is XON/XOFF. The XON character tells the receiver that the sender is ready to receive more data. The XOFF character tells the receiver to stop sending characters. The use of XON/XOFF is depreciated, it is preferable to use RTS/CTS flow control instead. |
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Stop bits are sent at the end of every byte transmitted in order to help the signal hardware at either end of the link resynchronise. There is a D/P/S conventional notation for specifying the software setup of a serial connection. 8/N/1 (very common) specifies 8 data bits, no parity, 1 stop bit. The number of data bits can be 7, 8, or (sometimes) 9. Parity can be none (N), odd (O), or even (E); the parity bit is borrowed from the data bits, so 8/E/1 means that one of the 8 data bits is used as the parity bit. There can be 1 or 2 stop bits (occasionally 0 I think). Other settings define when pins will send handshake signals, or other data integrity checks. The most common of these is XON/XOFF. The XON character tells the receiver that the sender is ready to receive more data. The XOFF character tells the receiver to stop sending characters. The use of XON/XOFF is deprecated, it is preferable to use RTS/CTS flow control instead. |
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