Measurement-computing Personal488 rev.3.0 For DOS & Windows 3.Xi Manual de usuario descargar pdf (Pagina 116)

II. SOFTWARE GUIDES - 8. Driver488/DRV 8K. Other Languages

Personal488 User’s Manual, Rev. 3.0 II-101

I/O Control (IOCTL) Communication

DOS provides several I/O Control (IOCTL) functions that are useful with Driver488/DRV. Two of

these:

IOCTL GetDeviceData

and

IOCTL SetDeviceData

allow Driver488/DRV to be configured

for faster “Raw Mode” communication, while the other two:

IOCTL Read

and

IOCTL Write

, perform

the functions of the BASIC

IOCTL$

function and

IOCTL#1

command, respectively.

IOCTL Get & Set Device Data

When communicating with character devices, DOS normally checks the transferred data for control

characters such as

X-ON

X-OFF

and

control-Z

. However when communicating with

Driver488/DRV, this is not desirable. First of all, it might interfere with control characters that are

supposed to be transferred to or from Driver488/DRV. Second, and more importantly, while DOS is

checking for control characters, it only transfers one character at a time to or from Driver488/DRV.

This is much less efficient than transferring large blocks of data. Thus, whenever possible, DOS should

be configured to not check for control characters when communicating with Driver488/DRV. This is

typically accomplished by a function called

RawMode

in the language-specific support files (such as

IEEEIO.C

) provided with Driver488/DRV. The DOS

IOCTL Get and SetDeviceData

functions

are used together to configure Driver488/DRV for

RawMode

(binary) communication as:

mov AX,4400h ;DOS Get Device Data Function

mov BX,ieee ;File handle for Driver488/DRV

int 21h ;Execute DOS function

mov DH,0 ;Must clear DH

or DL,20h :Set “don’t check for control characters” bit

mov AX,4401h ;DOS Set Device Data Function

mov BX,ieee ;File handle

int 21h ;Execute DOS function

The first part of this code fragment reads the current device control settings from DOS. These are

returned in the

Finally, DOS is again called to implement the new control settings. Once the

ieee

file has been

opened and configured for

RawMode

, we are ready to communicate with Driver488/DRV.

IOCTL Read & Write

IOCTL Read

and

IOCTL Write

provide a “back-door” communication channel to Driver488/DRV.

This alternate method of communication is normally used to send special commands (

Write

) and

request status (

Read

) from Driver488/DRV.

Driver488/DRV recognizes only one

IOCTL Write

command:

BREAK

. When

IOCTL Write

is used

to send

BREAK

to Driver488/DRV, it forces Driver488/DRV into a quiescent, ready state in which it is

waiting for a new command. The

BREAK

command also forces the

EOL OUT

terminators to their

default values. Thus Driver488/DRV is reset so that it is ready and able to receive new commands,

regardless of what it was previously doing.

It is recommended that the

BREAK

command be sent before any other Driver488/DRV commands. In

assembly language,

BREAK

may be sent as indicated in the table.

brk DB “BREAK” ;BREAK command text

brklen EQU $-brk ;Length of BREAK command

mov AX, 4403h ;IOCTL Write function

mov BX, ieee ;File handle

mov CX, brklen ;# chars to send

mov DX, offset

brk

;DS:DX -> command

int 21h ;Execute DOS function

jc error ;Check for error

This is identical to the BASIC command

IOCTL

described in “Section III: Command References” of

this manual.

The

IOCTL Read

command is used to receive status from Driver488/DRV. It receives a single ASCII

character, either

, or

. The meaning of each response is:

1 2 ... 111 112 113 114 115 116 117 118 119 120 121 ... 399 400

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