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Asynchronous Communications Migration by Bob DePeyster and Mike Genevro--Information Networks Division This article discusses migration from the ATP or ADCC subsystem on an MPE V system to the Distributed Terminal Subsystem (DTS) on an MPE XL system. The discussion includes comparisons of: * Physical appearance * Configuration * Supported devices * Terminal/printer types * Subsystem software characteristics PHYSICAL APPEARANCE The most physically apparent change in the terminal/printer subsystem, when migrating from MPE V to MPE XL, is the hardware configuration. The ATP/ADCC interface cards are placed directly in the SPU of MPE V systems. Therefore, the RS-232/422 cabling for asynchronous devices connects directly into the system cabinet. In comparison, MPE XL systems use Distributed Terminal Controllers (DTCs) connected as nodes on a LAN. The interface cards, to which the cables of devices are connected, reside in the DTC. In order to communicate with asynchronous devices, the SPU needs to hold only the interface card for the LAN. Although the physical environment of the terminal/serial printer subsystem on MPE XL systems looks very different from that of MPE V systems, the resulting functions and characteristics of the subsystem software are very similar. In fact, as long as an asynchronous device is supported on both systems, there should be very little difference between using the device on an MPE V system and using it on an MPE XL system. CONFIGURATION There are three areas of configuration that have changed from MPE V to MPE XL they are: General System Configuration With MPE V systems, the INITIAL/SYSDUMP utility is used to configure the system. MPE XL systems require you to use a utility called SYSGEN. SYSDUMP is an interactive program in which you answer questions to enter configuration information. SYSGEN is a command-based interactive program. Because you enter commands in SYSGEN instead of answering questions, you have more control over the process of entering configuration data. SYSGEN also has other advantages over SYSDUMP. For more information on SYSGEN, refer to the System Administrator's Migration Guide (P/N 30367-90003).
NOTE Note that SYSDUMP is used to configure the terminal/serial printer subsystem, whereas SYSGEN is not.
Terminal/Serial Printer Subsystem Configuration For MPE V systems, you must configure the asynchronous subsystem by assigning device characteristics one-by-one through the use of INITIAL/SYSDUMP dialogue questions. For MPE XL systems, you must use the Node Management Configuration Manager (NMMGR) to configure the Distributed Terminal Subsystem (DTS). With this configuration tool (NMMGR.PUB.SYS), device profiles are created. A profile is a set of characteristics, which is defined once and then may be used for as many devices as you wish. This shortens the time it takes to configure devices into the subsystem. For more information on configuration with NMMGR, refer to the configuration section of the Asynchronous Serial Communications System Administrator's Reference Manual (P/N 32022-90001), which begins with Chapter 8. Terminal Configuration Settings With MPE XL, the following configuration values must be set before a supported HP terminal will operate properly when connected to a DTC: * RecvPace (Receive Pacing) must be set to XON/XOFF. * XmitPace (Transmit Pacing) must be set to XON/XOFF. * BaudRate must be set at the speed configured for the terminal's port. The above settings are the only changes to the default device settings that are needed; all other settings may remain at the default values. (Note that the EnqAck setting may be left on although ENQ/ACK protocol is not used.) These special settings are not necessary for devices connected to MPE V systems. (Usually HP terminals will operate properly with all the default configuration settings.) Refer to Chapter 8 of the Asynchronous Serial Communications System Administrator's Reference Manual (P/N 32022-90001) for more information. SUPPORTED DEVICES The list of supported devices for MPE XL systems is different than the list of supported devices for MPE V systems. Refer to Chapter 4 of the Asynchronous Serial Communications System Administrator's Reference Manual (P/N 32022-90001) for the list of asynchronous devices that are supported on MPE XL systems. Terminal and Printer Type Comparisons The following Terminal Types are supported on the ATP and ADCC terminal/printer controllers with MPE V T-MIT or later (MPE V version G.01.00 or later): 6, 9, 10, 12, 13, 15, 16, 18, 19, 20, 21, 22, TTPCL18, TTPCL19, and TTPCL22 The DTS on MPE XL systems supports two Terminal Types: 10 and 18 and three Printer Types: 18, 21, and 22. The tables labeled "MPE XL Terminal Types Overview" and "MPE XL Printer Types Overview" provide an introduction to the MPE XL Terminal Types and Printer Types by comparing them to the MPE V Terminal Types that are the most similar. Refer to the "MPE XL Terminal Types Overview" table for the Terminal Types that apply to terminals, and to the "MPE XL Printer Types Overview" for the MPE V Terminal Types and MPE XL Printer Types that apply to printers. As you move devices from an MPE V system to an MPE XL system, refer to the tables labeled "Terminal Type Migration for Terminals" and "Terminal Type Migration for Printers" to decide which Terminal or Printer Type to use with each of your asynchronous devices. MPE XL Terminal Types Overview ------------------------------------------------------------------------------- | MPE XL Terminal | Similar MPE V | Differences | | Type | Terminal Type | | ------------------------------------------------------------------------------- | 10 | 10 | Enhanced XON/XOFF protocol on MPE | | | | XL. No ENQ/ACK protocol on MPE XL. | ------------------------------------------------------------------------------- | 18 | 18 | Enhanced XON/XOFF protocol on MPE | | | | XL. | ------------------------------------------------------------------------------- MPE XL Printer Types Overview ------------------------------------------------------------------------------- | MPE XL Printer | Similar MPE V | Differences | | Type | Terminal Type | | ------------------------------------------------------------------------------- | 18 | 18 | Enhanced XON/XOFF protocol on MPE | | | | XL. | ------------------------------------------------------------------------------- | 21, 22 | 21, 22 | Enhanced XON/XOFF protocol on MPE | | | | XL. No ENQ/ACK protocol on MPE XL. | | | | Printer initialization string of | | | | MPE V's TTPLC22 is used. Printer | | | | status checks are done less | | | | frequently on MPE XL; status | | | | requests are not sent after each | | | | printed line. | ------------------------------------------------------------------------------- Terminal Type Migration for Terminals ----------------------------------------------------------------------------------- | MPE V | Description | Use MPE XL | Comments | | Terminal | | Terminal | | | Type | | Type | | ----------------------------------------------------------------------------------- | 6, 9 | Non-HP hardcopy device | None | Devices that need delays | | | needing delays after | | are not supported on MPE | | | Linefeed or Formfeed. | | XL. | ----------------------------------------------------------------------------------- | 10 | General HP CRT terminal | 10 | Only XON/XOFF protocol is | | | using both ENQ/ACK and | | used on MPE XL. | | | XON/XOFF protocol. | | | ----------------------------------------------------------------------------------- | 12 | 8-bit character version | 10 | | | | of Terminal Type 10. | | | | | Used with languages that | | | | | need extended character | | | | | sets. | | | ----------------------------------------------------------------------------------- | 13 | Terminal Type 10 with no | None | These devices are not | | | echo or ENQ/ACK protocol. | | supported on MPE XL. | | | Used for plotters or the | | | | | HP 2601 printer. | | | ----------------------------------------------------------------------------------- | 15, 16 | 8-bit and 7-bit HP 2635 | None | The HP 2635 is not | | | hardcopy terminal. | | supported on MPE XL. | ----------------------------------------------------------------------------------- | 18 | Terminal Type 10 without | 18 | Terminal Type 18 is | | | ENQ/ACK protocol or a | | exactly the same on MPE V | | | read trigger. Used with | | and MPE XL except that an | | | non-HP devices. | | enhanced XON/XOFF | | | | | protocol is used on MPE | | | | | XL. | ----------------------------------------------------------------------------------- Terminal Type Migration for Printers ----------------------------------------------------------------------------------- | MPE V | Description | Use MPE XL | Comments | | Terminal | | Printer | | | Type | | Type | | ----------------------------------------------------------------------------------- | 18 | Non-HP devices or | 18 | MPE V's Terminal Type 18 | | | application printers. | | and MPE XL's Printer Type | | | | | 18 are exactly the same | | | | | except that an enhanced | | | | | XON/XOFF protocol is used | | | | | on MPE XL. | ----------------------------------------------------------------------------------- | TTPCL18 | Terminal Type 18 with a | 18 | The HP 2687A is not | | | printer initialization | | supported on MPE XL. | | | string and an XOFF timer. | | | | | Used with HP 2687A. | | | ----------------------------------------------------------------------------------- | 19 | Remote Serial Spooled | 21 | Status checking is done | | | Printer. | | less frequently on MPE | | | | | XL. The printer | | | | | initialization string is | | | | | the same as MPE V's | | | | | TTPCL22. | ----------------------------------------------------------------------------------- | TTPCL19 | PCL Remote Serial Spooled | 21 | Status checking is done | | | Printer. | | less frequently on MPE | | | | | XL. | ----------------------------------------------------------------------------------- | 20 | 8-bit Serial Spooled | 22 | Status checking is done | | | Printer. | | less frequently on MPE | | | | | XL. Initialization string | | | | | is the same as MPE V's | | | | | TTPCL22. | ----------------------------------------------------------------------------------- | 21 | Serial Spooled Printer | 21 | Status checking is done | | | with no status checking | | less frequently on MPE | | | after XOFF. | | XL. Initialization string | | | | | is the same as MPE V's | | | | | TTPCL22. | ----------------------------------------------------------------------------------- | 22 | 8-bit Serial Spooled | 22 | Status checking is done | | | Printer with no status | | less frequently on MPE | | | checking after XOFF. | | XL. Initialization string | | | | | is the same as MPE V's | | | | | TTPCL22. | ----------------------------------------------------------------------------------- | TTPCL22 | PCL 8-bit Serial Spooled | 22 | Status checking is done | | | Printer with no status | | less frequently on MPE | | | checking after XOFF. | | XL. | ----------------------------------------------------------------------------------- TERMINAL/PRINTER SOFTWARE CHARACTERISTICS The following are differences between the ASC software and the software that controls the ATP/ADCC. They include: * New Features. These are features that exist in the ASC software that do not exist in the software for ATP/ADCC. * Changed Functions. These are functions that have been implemented differently in the ASC software (and/or the DTC) from the way they are implemented for ATP/ADCC. * Programming Considerations. These are more functions that have been implemented differently. However, these functions apply only to programs written to control asynchronous devices. * Functions No Longer Supported. These are functions that are supported with the ATP/ADCC software, which are not supported with the ASC software.
NOTE The following pages document all known differences between the functionality of ATP/ADCC software and the functionality of ASC software. Some of the following differences are very detailed, but are not likely to impact the migration of most customer sites. They are included for completeness and for those customers who are knowledgeable enough in data communications to be interested in these details.
Changed Functions The following functions are implemented differently. Echo Facility Using [[ESCAPE]] is no longer necessary to turn the echo facility on or off. It is now accomplished with the MPE XL SET command. ([[ESCAPE]]: and [[ESCAPE]]; are not supported with the ASC software.) The syntax used to turn echo on or off is as follows: {ON } SET ECHO = {OFF} XON/XOFF Protocol With MPE V, XON/XOFF protocol is used, but there are certain cases when the XON (DC1) and XOFF (DC3) characters are ignored. Therefore, it is difficult to determine when these characters will be acted upon. With ASC software, these characters are always acted on when XON/XOFF protocol is enabled. Explanation. For instance, XOFF ([[CONTROL]]Son terminals) is ignored with MPE V during reads or when no I/O is pending on the device. (This means that nothing is waiting to be printed on the device and no program is waiting for input from the device.) With MPE XL, the [[CONTROL]]S character is never ignored (except during a binary read). Therefore, during a read, if [[CONTROL]]S is pressed, the read appears to be suspended. The [[CONTROL]]Q character must follow in order for the characters you typed to be echoed to the screen. Therefore, [[CONTROL]]Q must be typed in order to continue and complete the read. Another effect of having XON/XOFF protocol always enabled also involves using [[CONTROL]]S at a terminal. If a user has typed [[CONTROL]]S, the flow of data from the DTC to the terminal is halted because the DTC is waiting for an XON ([[CONTROL]]Q) from the terminal. This may cause a complication when the terminal is in trouble ("hung" ). It is common to use the ABORTIO command to cause the device to act normally again. With an MPE XL system, it is useless to send an ABORTIO to a terminal whose user has typed [[CONTROL]]S but not [[CONTROL]]Q. Therefore, while troubleshooting the terminal, type [[CONTROL]]Q at the keyboard before trying to use the ABORTIO command. If the ABORTIO command does not work after that, you may need to reset the terminal using TermDSM. For more information on troubleshooting and TermDSM, refer to the Asynchronous Serial Communications Troubleshooting Manual (P/N 32022-90004). Exception. The only exception to this is during binary mode. During a binary read, an ASCII DC1 or DC3 may be a data character and not intended as an XON or XOFF. Therefore, the ASC software does not react to them as if they are protocol characters, but passes them through as data. Since these characters are accepted as data, they will be echoed. However, when an XOFF is echoed, it will suspend the terminal as if an XOFF were sent to it from the DTC. This means that echo should be disabled while in binary mode in order to avoid this from happening.
NOTE Note that the XON/XOFF protocol characters are only accepted as data when coming from the device. When an ASCII DC1 or DC3 is sent from the DTC, the terminal will still react to the character as a protocol character.
Using Smooth Scroll A terminal uses its buffer to store incoming data and makes use of XON/XOFF protocol to keep the DTC from overflowing the terminal buffer. Some supported devices (namely the HP150 and HP293x terminals) support smooth scroll. When a device is in smooth scroll mode, it transfers data to its screen more slowly (in order to make the output look "smooth" ) and therefore uses its buffer more to store incoming data. This is especially true at higher speeds such as 9600 and 19,200 bps. As a terminal user, you are allowed to use XON/XOFF protocol to monitor what is written to the screen by pressing [[CONTROL]]S (XOFF) and [[CONTROL]]Q (XON). When both the terminal and its user are sending XONs and XOFFs to the DTC, the DTC has no way of knowing the source of the protocol characters. Therefore, it may appear that your [[CONTROL]]S and [[CONTROL]]Q characters are not being recognized. To avoid this problem, use the Stop key on your terminal instead of [[CONTROL]]S and [[CONTROL]]Q. When Stop is pressed, the terminal's buffer stops processing data, so no more will be printed to the terminal screen. When Stop is pressed a second time, the terminal will resume processing data in and out of its buffer. (Therefore, the Stop key functions as a toggle switch.) In this way, the terminal controls what protocol characters are sent to the DTC. You, as terminal user, do not also send protocol characters to the DTC because the Stop key does not send XON and XOFF characters to the DTC. Another way to alleviate the problem is to lower the terminal's transmission speed below 9600 bps. Devices running at 4800 bps or lower should not have this problem. Default Parity With MPE V and the ATP or ADCC, parity of a terminal is sensed during logon. Parity is not sensed with the ASC software of MPE XL; the default is to use 8-bit characters and no parity. This is true whether or not the device is a logon device or a programmatic device (such as a printer). Parity Error With ATP on MPE V, a read that contains a parity error must still complete normally. Then all read data is discarded. With DTC, the first parity error ends the read immediately and the read data is discarded. Parity error in EOR With ATP, a parity error in the EOR prevents the read from completing normally. Unless a timer expires or a byte count is satisfied, the device may hang. This is not a problem with DTC. The read completes when the parity error is detected and all data is discarded. Stripped Characters When the terminal controller reads input from a device, certain characters are searched for in the stream of data. When found, some of those are stripped from the data. The differences between the HP 3000 MPE V ATP and the ASC software in this area involve only three cases: * [[ESCAPE]]: This two-character sequence is not stripped from the input data on MPE XL systems. It is stripped from input data on MPE V systems. * [[ESCAPE]]; Same as [[ESCAPE]]:. * LF (Line feed). Line feeds are stripped from input data with MPE V. With MPE XL, line feeds are not stripped. Break and Terminal States When a Break is received, ATP saves EOR, Read Timer value, and terminal mode. Under the same circumstances, DTC saves all of these plus echo. Therefore, with ATP, if echo was disabled, it will be disabled in the CI. With DTC, echo is enabled at this time and then disabled when the user resumes. Using [[BREAK]] (and later RESUME) During a Read When you are entering data or a command in a subsystem and press [[BREAK]] (before pressing [[RETURN]]), MPE V keeps the data that you entered and completes the read if you re-enter the subsystem through the RESUME command. MPE XL disregards the read data. For example, you are in EDITOR, type LIST ALL and press [[BREAK]]. While in the MPE Command Interpreter, you enter SHOWTIME, read what time it is and then type in RESUME. You press [[RETURN]] at the READ Pending prompt. With MPE V, the data you entered before pressing [[BREAK]] is "remembered" and is immediately used as a command. Therefore, the LIST ALL is executed and the file you were editing will be listed out on the screen. With MPE XL, the read data is not remembered. After typing [[RETURN]] to the READ Pending prompt, a new read is started. The LIST ALL command is not acted upon. The Command Interpreter and [[BREAK]] During a read in the MPE V command interpreter, [[BREAK]] is disabled. It is not disabled in the MPE XL Command Interpreter. Preemptive Writes With MPE V, a preemptive write can interrupt a read or another write. With the ASC software on MPE XL systems, a preemptive write will only interrupt a read or a write not yet started, not a write that has already started. During Reads. You are using the command interpreter to type in MPE V commands on a terminal. You want to use the SHOWJOB command and begin typing. The system operator sends you a message via the WARN command after you have typed only the characters SH. The WARN message interrupts your read and is displayed on the screen. It is then necessary for you to begin typing the word SHOWJOB again because the SH was lost when the read was preempted by the message. With MPE XL, a WARN message will interrupt the read as if it were a WARN message on MPE V. However, in the example above, when you have typed SH of the SHOWJOB command and receive a WARN message, the SH is not lost. You only need to type OWJOB in order to execute the command. During Writes. On MPE XL, a preemptive write will not interrupt another write that has already started. Writes that have not yet started will be delayed until after the preemptive write. This is a very minor difference; you should see little change on this area between MPE V and MPE XL. Logical Console Functionality On all HP 3000 systems, the terminals other than the system console, can temporarily obtain partial console functionality via the CONSOLE command. This is called moving the logical console to a terminal. MPE V systems allow the logical console to receive console messages, execute normal console commands, and execute console commands that require the console attention character ([[CONTROL]]A). The functionality of the logical console on MPE XL systems is the same with one exception: the logical console may not execute console commands that require [[CONTROL]]A. The [[CONTROL]]A character is not recognized as the console attention character on any device other than the system console. For more information on the console, refer to Chapter 2 in the Asynchronous Serial Communications System Administrator's Reference Manual (P/N 32022-90001). Printer Status Request The printer status request, also known as status checking or the HP2631B handshake, is a means by which the controller keeps track of the condition of serial printers. Under MPE V, printer status checking may be done quite frequently. Terminal types 21 and 22 send a status request at FOPEN. With MPE XL systems, the timer is always enabled and measures every read. This means that: * There is no need to use FCONTROL 20. The timer is automatically enabled. * Obtaining the value of the read timer (FCONTROL 22) should happen before any other reads occur; otherwise, the value of the read timer will be for the most recent read, not the read that originally needed to be timed. * FCONTROL 21 cannot be used to disable the timer. (Making this intrinsic call has no effect on the timer.) Additional End-of-Record Characters With MPE V, any character may be used as an additional end-of-record character except for the list in the table labeled "Unrecognized Additional EOR Characters (MPE V)." With MPE XL, only the characters listed in the table labeled "Unrecognized Additional EOR Characters (MPE XL)" should not be used as additional end-of-record characters. You will receive no error messages if you use one of the characters in the table as an additional EOR, but the character will not terminate a read when a user enters it. For more information on end-of-record characters, refer to Chapter 3 of the Asynchronous Serial Communications System Administrator's Reference Manual (P/N 32022-90001). Unedited Mode On MPE V systems, the ASCII characters DC1 and DC3 are treated as data in unedited mode. With MPE XL, DC1 and DC3 are not treated as data, but as the protocol characters XON and XOFF. Binary Mode and Echo When initiating binary mode (FCONTROL 27) on an MPE XL system, turn echo off on the device (FCONTROL 13). This is necessary because if a DC3 character is in the data, it will be echoed and will XOFF the device. (Refer to "XON/XOFF Protocol" under "Changed Functions" earlier in this article.) Using FCONTROL 35 FCONTROL 35 is used to inhibit the printing of !!! (three exclamation points) when a user enters [[CONTROL]]X. When the !!! is disabled on MPE V systems, a carriage return and line feed is sent when a [[CONTROL]]X is received, all read data is disregarded, and the user may start typing the line from the beginning. On MPE XL systems, the [[CONTROL]]X functions the same except for one thing: the carriage return and line feed are not sent. Unrecognized Additional EOR Characters (MPE V) -------------------------------------------------------------------------------- | ASCII Character | Terminal Keys | Octal Code and Hex | | | | Code | -------------------------------------------------------------------------------- | NUL (Null) | [[Control]]@ | % 0 $ 0 | | BS (Backspace) | [[CONTROL]]H | % 10 $ 8 | | LF (Linefeed) | [[CONTROL]]J | % 12 $ A | | CR (Carriage Return) | [[CONTROL]]M | % 15 $ D | | DC1 (XON) | [[CONTROL]]Q | % 21 $11 | | DC2 | [[CONTROL]]R | % 22 $12 | | DC3 (XOFF) | [[CONTROL]]S | % 23 $13 | | CAN (Cancel) | [[CONTROL]]X | % 30 $18 | | EM (End-of-Medium) | [[CONTROL]]Y | % 31 $19 | | ESC (Escape) | [[CONTROL]][ | % 33 $1B | | DEL (Rubout) | | %177 $7F | -------------------------------------------------------------------------------- Unrecognized Additional EOR Characters (MPE XL) -------------------------------------------------------------------------------- | ASCII Character | Terminal Key | Octal Code and Hex | | | | Code | -------------------------------------------------------------------------------- | NUL (Null) | [[CONTROL]]@ | % 0 $ 0 | | BS (Backspace) | [[CONTROL]]H | % 10 $ 8 | | DC1 (XON) | [[CONTROL]]Q | % 21 $11 | | DC3 (XOFF) | [[CONTROL]]S | % 23 $13 | | CAN (Cancel) | [[CONTROL]]X | % 30 $18 | | Current Subsystem Break | [[CONTROL]]Y* | % 31 $19 | | DEL (Rubout) | DEL key | %177 $7F | -------------------------------------------------------------------------------- * In transparent mode, you define the subsystem break character through FCONTROL 41. Functions No Longer Supported The following functions that are supplied by the MPE V ATP/ADCC are not supported by the ASC software. ENQ/ACK Protocol This handshake between devices and the HP 3000 MPE V ATP/ADCC will not be supplied by the ASC software. Transmission Speeds of 110, 150, and 600 Since these speeds are rarely used on the HP 3000, the DTC will not support these speeds. Speedsensing With MPE V, the terminal controllers determine the transmission speed of a terminal during the logon process. This allows the terminal's speed setting to be different from the configured speed of the port to which the terminal is attached. Currently for the DTC, it is necessary that the speed setting of the terminal match the configured speed of the port. Even Parity Sensing With MPE V, the terminal controllers determine the parity of a terminal during the logon process by reading the value of the eighth bit of the initial carriage return. If this bit is one, even parity is used; if this bit is zero, no parity is used. The DTC does not use parity sensing; it is assumed that no parity is being used during logon. This means that devices set to use even parity should not be used and will not work properly. :EOF: Command The :EOF: command, which can be used to terminate a session or job on MPE V, is not supported on MPE XL. Carriage Control Delays Some older hard copy devices could not receive data quickly enough, especially when the carriage of the device had to move back to the beginning of the next line after each line was printed. MPE V supports terminal types that allow extra time for the device to prepare for the next line of output. It does this by providing extra time for each carriage return, line feed, and form feed that the device needed to perform. Since these devices are obsolete, HP does not provide this feature with the new terminal and printer types. Special Response to a Backspace Character Some devices require the terminal controller to handle the backspace character in a specific way. For instance, when a backspace is used on a hard copy device, a character typed after the backspace will be difficult to see because it will be typed directly over a previous character. Some MPE V terminal types reacted to a backspace by going to the next line, so that characters typed after a backspace would appear under, instead of on top of, previous characters. Since no devices that require this special attention are supported with the ASC software, no special response to the backspace character will be supplied. Our standard response to a backspace character is to echo the backspace to the terminal and delete the last character from the read data. Special Response to a Line feed Character The MPE V ATP/ADCC software will react to a line feed (LF) character by echoing a carriage return and line feed, then stripping the line feed from input data. The ASC software will not do this, and will not strip line feeds from input data. This is only different during line block mode. Special Output for a Formfeed Character For some devices, the MPE V ATP/ADCC software will substitute the line feed (LF) character for the form feed (FF) character. This will not be done by the ASC software. Critical Writes With MPE V, all writes to asynchronous printers are critical writes. This means that the file system reports the completion of the write to the program initiating the write only after the data from the write had been printed out. In other words, the write is complete only after the write is successful. With MPE XL, the completion of every write is reported by the file system when the DTC sends the data to the printer. Since this is before the data has actually printed, the completion of a write does not guarantee that the write was successful. Since the ASC software does not wait for each line to print before continuing, data can be sent to printers more quickly, improving the performance of printers on MPE XL systems. Workstation Configurator This product is not supported on MPE XL systems. FDEVICE CONTROL (Function 192) MPE XL systems do not support the use of Function 192 for the FDEVICE CONTROL intrinsic. Related Operating System Changes The following functionality of the MPE V operating system that is not supported on MPE XL has some significance for the asynchronous subsystem. MPE Commands The DATA and (command) commands, sometimes used to log on to terminals, are not supported on MPE XL. The JOB command, while still useful to stream jobs, cannot be used to log on to a terminal. File System Intrinsics The FCARD and PTAPE intrinsics, sometimes used with asynchronous devices, are not supported on MPE XL.