Software Characteristics

Pressing [Esc] is no longer necessary to turn the echo facility on or off. The MPE/iX :SET command is used now. The syntax used to turn echo on or off is as follows:

With MPE V, the XON/XOFF protocol is used, but certain cases exist when the XON (DC1) and XOFF (DC3) characters are ignored. Therefore, it is difficult to determine when these characters will be acted on. With ASC software, these characters are always acted on when the XON/XOFF protocol is enabled.

For instance, XOFF ([CTRL]-S on terminals) is ignored in 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/iX, the [CTRL]-S character is not ignored (except during a binary read).

Therefore, during a read, if [CTRL]-S is pressed, the read appears to be suspended. Press [CTRL]-Q to echo the characters typed to the screen. Therefore, [CTRL]-Q must be pressed to continue and complete the read.

The only exception is during binary mode. During a binary read, an ASCII DC1 or DC3 can be a data character and not an XON or XOFF. The ASC software does not react to them as if they are protocol characters, but passes them through as data. Since these protocol 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.

Note that the XON/XOFF protocol characters are accepted as data only 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.

A terminal uses its buffer to store incoming data and makes use of the 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 (to make the output look "smooth") and therefore uses its buffer to store more incoming data. This is especially true at higher speeds such as 9600 and 19,200 bps.

As a terminal user, use the XON/XOFF protocol to monitor what is written to the screen by pressing [CTRL]-S (XOFF) and [CTRL]-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 can appear that the [CTRL]-S and [CTRL]-Q characters are not being recognized.

To avoid this problem, press [Stop] instead of [CTRL]-S and [CTRL]-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 which protocol characters are sent to the DTC.

Another way to alleviate the problem is to lower the terminal's transmission speed; devices running at 4800 bps or lower will not have this problem.

With an ATP on MPE V, a read that contains a parity error still completes normally. Then, all read data is discarded. With a DTC, the first parity error ends the read immediately and the read data is discarded.

With an ATP, a parity error in the EOR character prevents the read from completing normally. Unless a timer expires or a byte count is satisfied, the device can hang. This is not a problem with a DTC. The read completes when the parity error is detected and all data is discarded.

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 MPE V ATP and the ASC software are as follows:

When a system break is received, the ATP saves the EOR character, the read timer value, and the terminal mode. Under the same circumstances, the DTC saves all of these, plus echo. Therefore, with ATP, if echo was disabled, it will be disabled in the Command Interpreter (CI). With the DTC, echo is enabled and disabled when the user resumes.

When you are entering data or a command in a subsystem and press [Break] (before pressing [Return]), MPE V keeps the data entered and completes the read if the :RESUME command is entered. MPE/iX disregards the read data.

Because of the speed with which MPE/iX systems process writes, more data can be lost if [Break] is entered while a program is writing to a terminal than was the case for terminals connected to MPE V systems.

During a read in the MPE V CI, [Break] is disabled. It is not disabled in the MPE/iX CI.

With MPE V, a preemptive write can interrupt a read or another write. With the ASC software on MPE/iX computers, a preemptive write will interrupt a read or a write not yet started, not a write that has already started.

On all HP 3000 computers, terminals other than the system console can temporarily obtain partial console functionality with 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 ([CTRL]-A).

The functionality of the logical console on MPE/iX computers is the same, with one exception: the logical console cannot execute console commands that require [CTRL]-A. The [CTRL]-A character is not recognized as the console attention character on any device other than the system console. (Do not attempt to move the logical console to a terminal connected via a PAD or to a terminal with switching enabled.)

The printer status request, also known as status checking or the HP2631B handshake, is how the controller monitors the condition of serial printers. Under MPE V, printer status checking can be done quite frequently. Terminal type files 21 and 22 send a status request at FOPEN, after each record is printed, and at FCLOSE. Terminal type files 19 and 20 send an additional status request every time the printer sends an XOFF. With MPE/iX printer type files 21 and 22, a status request is sent only at FOPEN and FCLOSE. (Neither MPE V terminal type 18 nor MPE/iX printer type 18 uses status checking.) Since status checking is done less frequently with MPE/iX, serial printers have better performance. (Printer type file 26 on MPE/iX functions the same as terminal type 26 file on MPE V.)

When programmatically changing the parity checking and generation of a specific connection (through the FCONTROL36 and FCONTROL24 intrinsics), the type of parity is determined by the value of a parameter of the FCONTROL36 intrinsic. The differences between MPE V's ATP and MPE/iX's DTC are listed in Table A-5 “Parity Settings with FCONTROL(36)”.

	NOTE: When a device is closed (using the FCLOSE intrinsic) on an MPE V computer, the initial default parity setting is restored. On MPE/iX computers, parity is not restored at FCLOSE. This means that to change parity using the FCONTROL intrinsic, the default parity in the application must be restored before closing the device.

On MPE V computers, the read timer must be enabled (FCONTROL20) before every read whose duration you wish to measure. With MPE/iX computers, the timer is always enabled and measures every read. This means the following:

With MPE/iX, the characters listed in Table A-6 “Unrecognized AEOR Characters (MPE/iX)” should not be used as additional end-of-record characters. An error message will not be received if one of the characters in the table is entered as an additional EOR, but the character will not terminate a read when it is entered. With MPE V, any character can be used as an additional end-of-record character, except for the list in Table A-7 “Unrecognized AEOR Characters (MPE V)”.

On MPE/iX computers, only one AEOR character can be designated for a device at any given time with FCONTROL(25), and multiple AEORs can be designated with FDEVICECONTROL(192,40).

On MPE V computers, the ASCII characters DC1 and DC3 are treated as data in transparent mode. With MPE/iX, DC1 and DC3 are not treated as data, but as the protocol characters XON and XOFF.

When initiating binary mode (through the FCONTROL27 intrinsic) on an MPE/iX computer, turn echo off on the device (FCONTROL13). 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 "Software Characteristics" earlier in this appendix for more information.

The FCONTROL35 intrinsic is used to inhibit the printing of !!! (three exclamation points) when the line deletion character ([CTRL]-X by default) is entered. When the line deletion response is disabled on MPE V computers, a carriage return and linefeed are sent when the line deletion request is received, and all read data is disregarded. The user can start typing the line from the beginning. On MPE/iX computers, the line deletion request functions the same except for one thing: the carriage return and linefeed are not sent.

MPE V computers, a limited number of device control functions can be modified through the FDEVICECONTROL intrinsic. On MPE/iX computers, FDEVICECONTROL has expanded device control functionality. Additionally, on MPE/iX computers, the FDEVICECONTROL intrinsic is supported for devices connected through a private or public PAD.

The ENQ/ACK protocol handshake between devices and the HP 3000 MPE V ATP/ADCC is not supplied by the ASC software.

The speeds 110 bps, 150 bps, and 600 bps are rarely used on the HP 3000 computer, so the DTC does not support them

The :EOF: and :EOD: commands, which can be used on MPE V computers, are not supported on MPE/iX computers.

Some hardcopy 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 type files 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, each linefeed, and the formfeed that the device must perform. Since these devices are obsolete, Hewlett-Packard does not provide this feature with new terminal type files and printer type files.

Some devices require the terminal controller to handle the backspace character in a specific way. For instance, when backspace is used on a hardcopy device, a character typed after the backspace will be difficult to see because it will be typed directly over the previous character. Some MPE V terminal type files react 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 devices that require this special attention are not supported with the ASC software, only two responses to the backspace character are supplied. Through the FDEVICECONTROL intrinsic, you can choose to either remove the character from input and back the cursor up one space, or to remove the character from input and erase it (backspace, space, backspace).

The MPE V ATP/ADCC software will react to a linefeed (LF) character by echoing a carriage return and linefeed, then stripping the linefeed from input data. The ASC software will not do this and will not strip linefeeds from input data. This is different during line block mode only.

For some devices, the MPE V ATP/ADCC software will substitute the linefeed (LF) character for the formfeed (FF) character. On MPE/iX computers, formfeed replacement is supported in carriage return, but not in user data.

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 has been printed out. In other words, the write is complete only after the write is successful. With MPE/iX, 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.

The :DATA and :COMMAND commands, sometimes used to log on to terminals, are not supported on MPE/iX. The :JOB command, while still useful to stream jobs, cannot be used to log onto a terminal.

The FCARD and PTAPE intrinsics, sometimes used with asynchronous devices, are not supported on MPE/iX.