nckary@ndsuvax.UUCP (Dan Kary) (09/21/85)
I have seen requests for an ibm pc termcap several times. This seems to be a point of confusion among some pc users. Termcap is the terminal capability data base, it contains descriptions of terminals in terms of what capabilities they have, the sizes of things like how many lines the screen displays and what sequence of characters must be sent to make the terminal perform some act, such as moving the cursor or clearing the screen. The ibm pc is not a terminal, and for that reason there is not and can not be a termcap entry that applies to the ibm pc. Frequently ibm pc's are used as terminals. This is accomplished by running a program that reads the keyboard and transmits the ascii value of the character that was typed over the rs-232 port while simultaneously reading the input of the rs-232 port and sending those characters to the screen. This program is frequently called a 'terminal emulator', because it makes an ibm pc (which is not a terminal) behave as if it were a terminal. In most video terminals the input data stream is interpreted; not all characters that are received are sent to the screen. Some sequences of characters cause actions to occur (move the cursor, clear the screen, etc.). The way the data stream is interpreted on the ibm pc (and thus, the termcap entry you need) is determined entirely by the terminal emulation software you are using. In the simplest case the terminal emulation software can do no data stream interpretation and send all charaters to the display. A program of this low a level of sophistication would probably be available for free. Commercial emulation software (and most freeware) will interpret the input data stream in the same manner that some popular terminal does. The most popular emulations (in my limited experience) are vt52 and vt100. It is also my experience that software emulators implement a subset of the emulated terminals capabilities. A correct termcap entry can be constructed by looking at your terminal emulator manual to see which terminal the software emulates. Find that entry in /etc/termcap, make a copy of that entry (with another name) and remove all the capabilities that terminal has that your emulator does not support (the technical section of your manual will optimistically list the capabilities it does support while ignoring the ones it does not support, so this may involve some effort). Lets consider the case where the emulation software does no data stream interpretation. Now the question is how is the data stream interpreted by the ibm pc? We send a data stream to a terminal over a communication line, how do we send a data stream to a pc? Well, we can get data from the keyboard or the disk or some other I/O device, but when does it get interpreted? If it gets interpreted at all, will depend both on the device it gets sent to and how it gets sent to that device. The device of interest is the screen, so now the question is how does data get sent to the screen? Ultimately, there is one way to put a character on the ibm pc screen, and that is to write the ascii value of the character into the display RAM of the display adapter. Programs usually do not do this directly, since they would have to know about the differences between the monochrome and color/graphics adapters. Usually the BIOS is used to put characters on the screen. BIOS means Basic Input and Output System; it is software contained within the imb pc's ROM. The BIOS knows how to put characters into the display RAM of both types of adapters so other programs don't have to worry about that particular detail. Simply tell BIOS which character to display and it does the job. The BIOS does not do any data stream interpretation (unless you consider translating 'carriage return' or 'line feed' into what amounts to be a cursor move to be 'interpretation'). If you send a sequence of characters to the BIOS that would cause the cursor to move if that same sequence were sent to a vt100, you will see some graphic characters and perhaps some alphanumeric characters displayed. Moving back one level, we can also send characters to the screen by using MS-DOS. Simply tell MS-DOS which character(s) to display and it will translate this request into one or more BIOS requests to display the characters. This description also gives some indication of the issues involved in 'ibm pc compatibility'. If a program makes only MS-DOS requests only thru MS-DOS defined entry points, it will run on any machine that runs MS-DOS. Likewise, any program that uses BIOS facilities will run on machines that have an ibm compatible BIOS. Programs which write directly to the ibm hardware will work only with hardware that is functionally identical to ibm's. MS-DOS 2.1 as distributed by IBM (and most compatibles) includes a device driver called ANSI.SYS, which is a data stream interpreter which makes an ibm pc (in an *extremely* limited sense) behave as a vt100 (ANSI X3.64) terminal. ANSI.SYS is installed by creating a file named CONFIG.SYS which includes the line: DEVICE=ANSI.SYS This line causes the file named ANSI.SYS to be installed as a device driver. This device driver causes some MS-DOS requests (int 21h and int 40h(or there abouts)) to be rerouted to this driver. ANSI.SYS then looks to see if the data is intended for the screen, if it is intended for the screen, then ANSI.SYS looks to see if one of the pre-defined 'Escape sequences' is being sent. ANSI.SYS translates the data stream into BIOS requests for cursor movement, print character or whatever. I hasten to add that ANSI.SYS works ONLY with screen requests that use the MS-DOS mechanisms for writing to the screen. Programs that use BIOS calls or write directly to the display adapter will be unaffected by this device driver. Finally, at long loving last, I can say that I have a termcap entry that is in some extended sense 'for the ibm-pc-xt' (it is in fact specific to ANSI.SYS). This could be used with a terminal emulator that did no data stream interpretation *if* that emulator uses the MS-DOS entry points. ansi.sys|IBM PC with ANSI.SYS installed as a device driver:\ :co#80:li#25:cl=\E[2J:\ :bs:am:cm=\E[%i%d;%dH:do=\E[B:nd=\E[C:up=\E[A:\ :so=\E[7m:se=\E[0m:kb=^H:\ :ce=\E[K:ho=\E[H:pt: Dan Kary North Dakota State University Computer Science Department 300 Minard Hall Fargo, ND 58102 ihnp4!dicomed!nckary
jabusch@uiucdcsb.CS.UIUC.EDU (09/29/85)
Actually, there *is* a termcap for the IBM-PC family for using a
PC without a terminal emulator or the ANSI.SYS driver. It's 'sd'. :-)
John W. Jabusch
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