Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 192)

II. SOFTWARE GUIDES - 9. Driver488/SUB 9H. Data Transfers
Personal488 User’s Manual, Rev. 3.0 II-177
two characters are specified, without EOI , all the characters up to, but not including, the Term input
terminator characters, are returned to the program. However, if both EOI and characters are specified,
the following considerations apply:
•
If EOI is received, and the complete terminator character sequence has not been received (even if
the first of the two characters has been received), then all the received characters are returned to
the program.
•
If the complete terminator character sequence has been received, with or without EOI asserted on
the last character, then only the characters up to but not including the terminator characters are
returned.
•
If only one character is specified for input termination, the complete terminator character sequence
consists of just that one character, but if two characters are specified, then it consists of both
characters, received consecutively.
During normal Output , without a specified character count, the Term output terminator is appended to
the data before sending the data to the bus devices. During normal Enter , the Term input terminator
received by Driver488 is stripped off before being returned to the program. See the Enter and
Output commands in the following text, and in “Section III: Command References.”
Data Input and Output
When a program performs data I/O through Driver488, it tells Driver488 where in memory to find or
put the data and the amount of data to transfer. Driver488 handles the actual transfer. The program
sends the address and quantity of data to be transferred, and Driver488 takes care of the details of the
transfer. The program must be able to tell Driver488 where in memory to find the data, that is, it must
be able to provide Driver488 with the actual address of the buffer. In C language, a character array is
usually used at the memory location for the incoming or outgoing data:
char buffer [20];
The following is a typical EnterX command:
char buffer [20]
EnterX (dev, buffer, sizeofbuffer, 1, 0L, 0, 0L);
The Driver488 EnterX command addresses the ADC bus device ( dev ), requests Driver488 to read 20
bytes of data and put the received data in the buffer memory location. This gives Driver488 all the
information it needs to be able to transfer the received data directly into the buffer character array.
Data I/O using the Driver488 OutputX command is also possible. For instance, suppose the data from
the above example was to be sent to a device called DAC . Here, we would use the following command:
OutputX (DAC, buffer, sizeofbuffer, 1, 0L, 0, 0L);
Data I/O is normally performed with terminator detection set to the default values of carriage-return
line-feed (
CR LF ) with end-or-identify ( EOI ). However, it is possible to explicitly specify that the
Enter should stop on detection of EOI only, or on detection of EOI or some single character. For
example, to terminate on EOI :
term.eoi=1;
term.nChar=0;
EnterX (dev, buffer, sizeofbuffer, 1, &term, 0 0L);
This reads data into the buffer character array until either 20 characters have been received, or EOI has
been detected. However, if EOI causes the transfer to stop, we may need to know how much data was
received. This information can be obtained by using the Buffered command:
N=Buffered(dev)
The number of bytes transferred is read into N . This value can now be used to send the read data out to
the device ( dev ), as follows:
OutputN (dev, buffer, N, 1, &term, 0, 0L);
Note that the variable N has been used in place of the literal 20 to specify how many bytes to transmit.