Specifications

Instrument Model and Command Processing ZVx
1043.0009.50 3.146 E-15
3.7 Instrument Model and Command Processing
The model shown in Fig. 3-2 visualizes the instrument from the point of view of servicing IEC-bus
commands. The individual components work independent of each other and simultaneously. They
communicate with each other by means of so-called "messages".
IEC Bus
Command
recognition
Data set
Instrument
hardware
IEC Bus
Output unit with
output buffer
Input unit with
input puffer
Status reporting-
system
Fig. 3-2 Model of the instrument in the case of remote control by means of the IEC bus
3.7.1 Input Unit
The input unit receives commands character by character from the IEC bus and collects them in the
input buffer. The input buffer has a size of 256 characters. The input unit sends a message to the
command recognition as soon as the input buffer is full or as soon as it receives a delimiter,
<PROGRAM MESSAGE TERMINATOR>, as defined in IEEE 488.2, or the interface message DCL.
If the input buffer is full, the IEC-bus traffic is stopped and the data received up to then are processed.
Subsequently the IEC-bus traffic is continued. If, however, the buffer is not yet full when receiving the
delimiter, the input unit can already receive the next command during command recognition and
execution. The receipt of a DCL clears the input buffer and immediately initiates a message to the
command recognition.