Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 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
DX register which is then modified to tell DOS not to check for control characters.
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 0 , 1 , 2 , or 3 . The meaning of each response is: