Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 128)

II. SOFTWARE GUIDES - 8. Driver488/DRV 8M. Data Transfers
Personal488 User’s Manual, Rev. 3.0 II-113
EOL OUT NONE does eliminate the inconvenience of appending terminators to Driver488/DRV
commands, but it does require that the entire command be contained in one transfer. Without EOL OUT
NONE it is possible to split a long Driver488/DRV command into several, smaller phrases:
ieeewt(“ENTER 16 #1000 ”);
ieeewt(“BUFFER &HB800:0 ”);
ieeewt(“CONTINUE\n”);
which would have to be combined into a single transfer with EOL OUT NONE :
ieeewt(“ENTER 16 #1000 BUFFER &HB800:0 CONTINUE”);
TERM Terminators
Just as the EOL terminators delimit the end of strings transferred between the user’s program and
Driver488/DRV, the TERM terminators delimit the end of strings transferred between Driver488/DRV
and bus devices. The TERM output terminator marks the end of strings transferred from
Driver488/DRV to bus devices, and the TERM input terminator marks the end of strings transferred into
Driver488/DRV from bus devices.
The TERM terminators differ from the EOL terminators in one important aspect. While the EOL
terminators are composed of one or two characters, the TERM terminators can include the IEEE 488 bus
end-or-identify ( EOI ) signal. The EOI signal, when asserted during a character transfer, marks that
character as the last of the transfer. This allows the detection of the end of data regardless of which
characters comprise the data. This feature is very useful in binary data transfers which might contain
any ASCII values from
0 to 255 .
To support the EOI signal, the TERM input and output terminators can be composed of just EOI , one or
two characters, or one or two characters with EOI . If EOI is specified, it has a slightly different
meaning on input than on output.
When EOI alone is specified as the TERM output terminator, the EOI bus signal is asserted during the
last data character transmitted. If EOI is specified with one or two characters, then EOI is asserted on
the last of the characters. In this way, EOI is asserted on the last character transmitted to the bus
device.
When EOI alone is specified as the TERM input terminator, then all the characters received from the bus
device, including the one on which EOI was asserted are returned to the user’s program. When one or
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 or buffer, the EOL output terminator
received by Driver488/DRV is replaced by the TERM output terminator before sending the data to the
bus devices. During normal ENTER , the TERM input terminator received by Driver488/DRV is replaced
with the EOL input terminator before being returned to the program. In this way, the program
communicates with Driver488/DRV using the EOL terminators, and Driver488/DRV communicates
with bus devices using the TERM terminators.
See the ENTER and OUTPUT command descriptions in the following text, and in “Section III: Command
References” for more information.