C5DG-9 Terminal Drivers

Clipper 5.x – Drivers Guide

Chapter 9

Alternate Terminal Drivers

Clipper supports a driver architecture that allows Clipper- compiled applications to use alternate terminal drivers. This architecture provides support for nonstandard video hardware and ANSI output devices, allowing your applications to run in a wider variety of environments.

The following terminal drivers are supplied as part of the Clipper Development System and are discussed in this chapter:

. The ANSITERM driver provides ANSI terminal support for systems that require it

. The NOVTERM driver causes Clipper applications to execute faster when run on some nondedicated network server software

. The PCBIOS driver provides direct BIOS calls rather than direct screen writes for systems requiring this form of I/O

In This Chapter

This chapter discusses how Alternate Terminal Drivers fit into the overall Clipper architecture as well as how to install and use each of the supplied terminal drivers. The following major topics are discussed:

. The Alternate Terminal Driver Architecture

. The ANSITERM Alternate Terminal Driver

. The NOVTERM Alternate Terminal Driver

. The PCBIOS Alternate Terminal Driver

The Alternate Terminal Driver Architecture

In Clipper, communication with I/O devices is controlled by a multilayered terminal system. At the lowest level is the terminal driver which controls screen and keyboard activity. It consists of a screen and keyboard driver that communicates directly with the I/O device (operating system or hardware). It is the device specific part of the Clipper terminal system.

There is, then, a higher level system that communicates with terminal drivers. This system is known as the General Terminal (GT) system and provides general services that create Clipper screen and keyboard commands and functions. The following figure demonstrates:

                   +—————————————–+

                   | CA-Clipper screen and keyboard commands |
                   |              and functions              |
                   |-----------------------------------------|
                   |        General Terminal (GT.OBJ)        |
                   ------------------------------------------|
                   |             Terminal Driver             |
                   |-----------------------------------------|
                   |          Screen   |   Keyboard          |
                   +-----------------------------------------+

The default terminal driver, designed for IBM PC and 100% compatibles, is supplied as a library file (TERMINAL.LIB) installed into your \CLIPPER5\LIB directory. This driver links into each program automatically if you specify no alternative terminal driver provided that you do not use the /R option when you compile. An alternate terminal driver is supplied as a separate library (.LIB) file that links into an application program in place of the default terminal driver if you specify it on the link line.

All alternate terminal drivers work through the General Terminal layer as supplied in the file GT.OBJ. The Clipper installation program installs this file in the \CLIPPER5\OBJ subdirectory on the drive that you specify, so you need not install the driver manually.

The ANSITERM Alternate Terminal Driver

The ANSITERM terminal driver supports the ANSI screen mode for all screen display from Clipper programs.

This screen mode is installed by specifying ANSI.SYS in the user’s CONFIG.SYS. ANSI.SYS replaces the default DOS CON device driver for video display and keyboard input. Once installed it supports ANSI escape sequences to erase the screen, set the screen mode, and control the cursor in a hardware-independent way. Most modern DOS programs, however, do not use it and write either directly to the video hardware or use BIOS routines for enhanced screen performance.

Use the ANSI screen mode for Clipper programs that run on hardware that does not support either writing to video hardware or BIOS calls for screen display. This is the case when using alternative display hardware to support the blind.

Note: The ANSITERM terminal driver fully supports all screen and keyboard functionality of the default terminal driver. This includes the ability to save and restore screens and support for all keys on the standard 101-key keyboard.

Installing ANSITERM Terminal Files

The ANSITERM terminal driver is supplied as the file ANSITERM.LIB. The Clipper installation program installs this file in the \CLIPPER5\LIB subdirectory on the drive that you specify, so you need not install it manually.

Linking the ANSITERM Terminal Driver

To link the ANSITERM alternate terminal driver into an application program, you must specify both GT.OBJ and ANSITERM.LIB to the linker along with your application object (.OBJ) modules.

1. To link with .RTLink using positional syntax:

C>RTLINK <appObjectList> GT,,, ANSITERM

2. To link with .RTLink using freeformat syntax:

C>RTLINK FI <appObjectList>, GT LIB ANSITERM

3. To link with .RTLink using ANSITERM.PLL and freeformat syntax:

C>RTLINK FI <appObjectList> /PLL:ANSITERM

Note: These link commands assume you have set the LIB, OBJ, and PLL environment variables to the standard locations. They also assume that the Clipper programs were compiled without the /R option.

Important! You cannot link the ANSITERM driver with BASE52.PLL. An application linked with both ANSITERM.LIB and BASE52.PLL may cause the computer to freeze upon execution.

The Runtime Environment

Using ANSITERM.LIB requires that ANSI.SYS be installed on the user’s computer. To accomplish this, include the following statement in the user’s CONFIG.SYS:

DEVICE=ANSI.SYS

Performance Concerns

Because the ANSITERM terminal driver uses buffered screen writes for all screen painting, some operations, especially those that scroll the screen, are slow. These include:

1. All box drawing commands and functions

2. All console commands and functions when scrolling

3. All clear screen commands and functions

4. All restore screen commands and functions

5. Standard out functions (OUTSTD() and OUTERR()) whether the screen is scrolling or not

Note: Overall performance of Clipper programs is slower since the ANSITERM terminal driver must spend more time polling for user events than the standard Clipper terminal driver.

Screen Output from C and Assembly Language

The ANSITERM terminal driver overwrites all output from C and Assembly Language when it refreshes the screen from the screen buffer. As a consequence, you should perform all screen output from Clipper.

The ANSITERM terminal driver also virtualizes the cursor. This means that BIOS functions that report the location of the hardware cursor will not always return the correct value. To obtain the cursor position, use Clipper’s ROW() and COL() functions instead.

Other Incompatibilities

1. ISCOLOR() always returns false (.F.).

2. When you load DBU, the default color mode is monochrome unless you specify DBU with the /C command line option.

3. The first time you invoke the Debugger, the default color mode is also monochrome unless you set the Options:Mono display off.

4. When an application linked with the ANSITERM terminal driver terminates, the last color set in the application becomes the DOS color. This happens since colors set with ANSITERM are global to DOS and Clipper cannot query DOS for the current screen colors as the application loads.

5. Nondisplaying ASCII characters are presented as a space by the ANSITERM terminal driver. These include BELL (CHR(7)), BS (CHR(8)), TAB (CHR(9)), LF (CHR(10)), CR (CHR(13)), and ESC (CHR(27)).

The NOVTERM Alternate Terminal Driver

The NOVTERM terminal driver is a special-purpose driver that circumvents an incompatibility between some nondedicated network server software and Clipper. This incompatibility causes printers connected to the server to slow to an unusable rate.

Clipper applications and nondedicated servers compete for resources. Clipper applications make use of the time between keystrokes to perform various system tasks. This greatly improves the application’s overall performance by limiting its idle time. Certain nondedicated servers only attempt to print within an application’s idle time. Since a Clipper application is seldom idle, this greatly slows printing.

Important! The NOVTERM terminal driver corrects the incompatibility by preventing the Clipper application from using idle time. Because this can severely hamper performance, you should only use the NOVTERM terminal driver when necessary, and then you should link it only into those applications that are physically running the nondedicated server.

Note: The NOVTERM terminal driver fully supports all screen and keyboard functionality of the default terminal driver. This includes the ability to save and restore screens and support for all keys on the standard 101-key keyboard.

Installing NOVTERM Terminal Files

The NOVTERM terminal driver is supplied as the file NOVTERM.LIB. The Clipper installation program installs the driver file in the \CLIPPER5\LIB subdirectory on the drive that you specify, so you need not install it manually.

Linking the NOVTERM Terminal Driver

To link the NOVTERM alternate terminal driver into an application, you must specify both GT.OBJ and NOVTERM.LIB to the linker with your application object (.OBJ) modules.

1. To link with .RTLink using positional syntax:

C>RTLINK <appObjectList> GT,,, NOVTERM

2. To link with .RTLink using freeformat syntax:

C>RTLINK FI <appObjectList>, GT LIB NOVTERM

3. To link with .RTLink using NOVTERM.PLL and freeformat syntax:

C>RTLINK FI <appObjectList> /PLL:NOVTERM

Note: These link commands assume you have set the LIB, OBJ, and PLL environment variables to the standard locations. They also assume that the Clipper programs were compiled without the /R option.

Important! You cannot link the NOVTERM driver with BASE52.PLL. An application linked with both NOVTERM.LIB and BASE52.PLL may cause the computer to freeze upon execution.

Performance Concerns

Overall performance of Clipper programs is slower since the NOVTERM terminal driver must spend more time polling for user events than the standard Clipper terminal driver and since the program will not use its idle time for other tasks.

Screen Output from C and Assembly Language

The NOVTERM terminal driver overwrites all output from C and Assembly Language when it refreshes the screen from the screen buffer. Therefore, you should perform all screen output from Clipper.

The NOVTERM terminal driver also virtualizes the cursor. This means that BIOS functions that report the location of the hardware cursor will not always return the correct value. To obtain the cursor position, use Clipper’s ROW() and COL() functions.

The PCBIOS Alternate Terminal Driver

The PCBIOS terminal driver uses BIOS calls instead of direct screen writes. It is designedd for applications that trap BIOS calls to redirect output over telecommunication lines or to convert output to a form compatible with two-byte character sets.

Note: The PCBIOS terminal driver fully supports all screen and keyboard functionality of the default terminal driver. This includes the ability to save and restore screens and support for all keys on the standard 101-key keyboard.

Installing PCBIOS Terminal Files

The PCBIOS terminal driver is supplied as the file, PCBIOS.LIB. The Clipper installation program installs the driver file in the \CLIPPER5\LIB subdirectory on the drive that you specify, so you need not install it manually.

Linking the PCBIOS Terminal Driver

To link the PCBIOS alternate terminal driver into an application program, you must specify both GT.OBJ and PCBIOS.LIB to the linker in addition to your application object (.OBJ) modules.

1. To link with .RTLink using positional syntax:

   C>RTLINK <appObjectList> GT,,, PCBIOS;

2. To link with .RTLink using freeformat syntax:

   C>RTLINK FI <appObjectList>, GT LIB PCBIOS

3. To link with .RTLink using PCBIOS.PLL and freeformat syntax:

   C>RTLINK FI <appObjectList> /PLL:PCBIOS

Note: These link commands assume you have set the LIB, OBJ, and PLL environment variables to the standard locations. They also assume that the Clipper programs were compiled without the /R option.

Important! You cannot link the PCBIOS driver with BASE52.PLL. An application linked with both PCBIOS.LIB and BASE52.PLL may cause the user’s computer to freeze when the user executes it.

Performance Concerns

Because the PCBIOS terminal driver uses buffered screen writes for all screen painting, some operations, especially those that scroll the screen, are slow. These include:

1. All box drawing commands and functions

2. All console commands and functions when scrolling

3. All clear screen commands and functions

4. All restore screen commands and functions

5. Standard out functions (OUTSTD() and OUTERR()) whether the screen is scrolling or not

Screen Output from C and Assembly Language

The PCBIOS terminal driver also overwrites all output from C and Assembly Language when it refreshes the screen from the screen buffer. Therefore, you should perform all screen output from Clipper.

The PCBIOS terminal driver also virtualizes the cursor. This means that BIOS functions that report the location of the hardware cursor do not always return the correct value. To obtain the cursor position, use Clipper’s ROW() and COL() functions.

Summary

This chapter has introduced you to the Alternate Terminal Driver concept, giving you specific information on the architecture used to implement them in Clipper. Each of the alternate terminal drivers supplied with Clipper was discussed, including how to link and use it into your application and the implications of doing so.

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Format of xBase Files

xBase File Format Description

xBase File Types

xBase File  Types and Extensions

Ext. File Type  Introduced or used by
.$$$ temporary file  dBASE III
.$db temporary file  dBASE IV
.act FoxDoc Action Diagrams  FoxPro
.app application object file  dBASE Appl. Generator
.app generated application  FoxPro
.bak Backup file  dBASE
.bar horizontal bar menu object file  dBASE Appl. Generator
.bin Binary files  dBASE
.bch batch process object file  dBASE Appl. Generator
.cac executable when caching on/off  dBASE IV
.cat catalog  dBASE III, IV
.cdx compound index  FoxPro
.ch header file  Clipper
.cht interface file for ChartMaster  dBASE
.clp compiler script file (clip list)  Clipper
.cmd command  dBASE – Waffle
.cod template source file  dBASE Appl. Generator
.cpt encrypted memo file  dBASE
.crp encrypted database  dBASE IV
.ctl control file  dBASE IV – Aldus Setup
.cvt backup file for CONVERTed database file  dBASE IV
.db configuration  dBASE
.db$ temporary file  dBASE
.db2 database  dBASE II
.db3 database  dBASE III
.dbf database file  dBASE – FoxPro
.dbk database backup  dBASE IV
.dbo compiled program  dBASE IV
.dbt FoxBASE+ style memo  FoxPro
.dbt memo file for database w/same name  dBASE – Clipper
.def Definitions list  dBASE
.dif Data Interchange Format. For APPEND FROM, COPY  dBASE – VisiCal
.doc Documentation text file  dBASE Appl. Generator
.fil files list object file  dBASE Appl. Generator
.fky macro file  FoxPro
.fmo compiled format file  dBASE IV
.fmt format file  dBASE – FoxPro – Clipper
.fp configuration file  FoxPro
.fpc catalog  FoxPro
.fpt memo  FoxPro
.fr3 renamed dBASE III+ form file  dBASE IV
.frg uncompiled report file, code fragment file  dBASE IV
.frm report file  dBASE – Clipper
.fro compiled report file  dBASE IV
.frt report memo  FoxPro
.frx report  FoxPro
.fw2 Framework spreadsheet or database file  Framework – dBASE
.fxp compiled format  FoxPro
.gen compiled template  dBASE Appl. Generator
.idx index (many)  FoxPro
.ind include index  dBASE IV
.inx index  FoxBase
.key Key macro library  dBASE
.lbg label generator data  dBASE IV
.lbl label  dBASE – Clipper
.lbo compiled label  dBASE IV
.lbt label memo  FoxPro
.lbx label  FoxPro
.ld1 overlay file  dBASE
.log Transaction log file  dBASE
.mbk multiple index file backup  dBASE IV
.mdx multiple index file  dBASE IV
.mem memory variable save file  dBASE – FoxPro
.mnt menu memo  FoxPro
.mnx menu  FoxPro
.mpr generated program  FoxPro
.mpx compiled menu program  FoxPro
.ndx index file  dBASE
.npi source for DGEN.EXE interpreter  dBASE Appl. Generator
.ntx index file  Clipper
.pjt project memo  FoxPro
.pjx project  FoxPro
.plb library  FoxPro
.pll pre-linked library  Clipper
.plt pre-linked transfer file  Clipper
.pop pop-up menu object  dBASE Appl. Generator
.ppo pre-processor output  Clipper
.pr2 printer driver  dBASE IV
.pr3 PostScript printer driver  dBASE IV
.prf printer driver  dBASE IV
.prg program source file  dBASE – FoxPro – Clipper
.prs procedure  dBASE IV
.prt Print dump  dBASE
.prx compiled program  FoxPro
.qbe saved query (Query By Example)  dBASE IV – Quattro Pro
.qbo compiled query  dBASE IV
.qpr generated query program  FoxPro
.qpx compiled query program  FoxPro
.qry query  dBASE IV
.res dBASE resources  dBASE IV
.rpd Rapid file. For IMPORT/EXPORT,APPEND  FROM, COPY  dBASE
.sc3 renamed dBASE III screen mask file  dBASE IV
.scr screen – screen snapshot  dBASE IV
.sct screen memo  FoxPro
.scx screen  FoxPro
.spr generated screen program  FoxPro
.spx compiled screen program  FoxPro
.str structure list object file  dBASE Appl. Generator
.t44 Temporary file for Sort or Index  dBASE IV
.tbk memo backup  dBASE IV – FoxPro
.tvf table view settings  dBASE
.upd update data  dBASE
.upo compiled update data  dBASE
.val values list object file  dBASE Appl. Generator
.vew view file  Clipper, Lotus Approach
.vue view  dBASE IV – FoxPro
.w44 temporary file for Sort or Index  dBASE
.wfm form object  dBASE Form Designer
.win window file  FoxPro – dBASE

Source :  http://www.clicketyclick.dk/databases/xbase/format/index.html

Notes:

–          Such a list can’t be perfect. Some item may be obsolete / forgotten and something may not exist when this list compiled.

–          “Clipper” may not include all versions of Clipper.

–          Most of Clipper files are supported by Harbour.