IBM 7220, Instruction Manual

Page: 55 / 155

5-15
Chapter 5, FRONT PANEL OPERATION
5.2.10 GPIB Setup 2 Menu
Figure 5-11, GPIB Setup 2 Menu
This menu, shown in figure 5-11, has two controls affecting the GPIB computer
interface, as follows:-
SRQ Mask
The instrument includes the ability to generate a Service Request on the GPIB
interface, to signal to the controlling computer that urgent attention is required. The
request is generated when the result of a logical bit-wise AND operation between the
Service Request Mask byte, set by this control, and the instrument’s Status Byte, is
non-zero. The bit assignments of the Status Byte are as follows:-
Bit Decimal value Function
0 1 command complete
1 2 invalid command
2 4 command parameter error
3 8 reference unlock
4 16 overload
5 32 auto-mode active or new ADC values available after
external trigger
6 64 asserted SRQ
7 128 data available
Hence, for example, if the SRQ mask byte is set to decimal 16 (i.e. bit 4 is asserted),
a service request would be generated as soon as an overload occurred; if the SRQ
mask byte were set to 0 (i.e. no bits asserted), then service requests would never be
generated.
Test echo
When this control is enabled, all transmissions to and from the instrument via the
GPIB interface are echoed to the RS232 interface. Hence if a terminal is connected to
the latter port, it will display any commands sent to the instrument and any responses
generated, which can be useful during program development. When disabled, echoing
does not occur. The control should always be disabled when not using this feature,
since it slows down communications.