HP 3468A - Page 80

Front Panel SRQ When this bit is set to a 1 it indicates that the front panel
Bit
4
SRO
button
has
been
pressed.
This
bit
is
cleared
when
the
3468A is Serial Polled.
Calibration Fail This bit is used to indicate that an attempted calibration has
Bit 5 failed. The bit will be set to 1 under this condition. A Serial
Poll will clear this bit.
Require
Service
This
bit
is
set
to
1
whenever
one
of
the
events
specified
for
Bit 6 bits O through 5 above occurs at the same time that the cor-
responding
bit
in
the
mask
register
is
set.
The
bit
is
also
set
at
power-on
or
when
Test/Reset
is
executed
if
the
PON
SRO
switch
on
the
rear
panel
is
turned
on.
This
bit
is
cleared
only
when the conditions
for requesting
service no longer exist, i.e.
bits 1-5 and 7 are cleared.
Power-on Reset This bit is set to 1 when a power-on reset has occurred. If
Bit 7 switch 3 on the rear panel block of switches is set to the “1”
or
up
position,
bit
6
will
be
true
and
the
SRO
message
is
sent.
Bit 7 is cleared when the 3468A is Serial Polled.
The Status Byte together with the Service Request (SRQ) Mask determine when
the Require Service (ROS) bit is to be set. Setting ROS causes SRO to be sent on
the HP-IL. A Serial Poll of the 3468A will clear SRO and it will remain clear until
another reason for setting ROS occurs. ROS on the other hand, is set if one or
more corresponding bits in the Status Byte and SRO Mask are both set. RQS is
cleared whenever all corresponding bits are not both set. A Serial Poll then, may
cause ROS to be cleared but not in all cases. Bits 2, 4, 5, and 7 are cleared with
a Serial Poll.
Try this simple exercise.
1. Reset the 3468A. This should be done by cycling the LINE switch. Without
setting the SRQ mask, perform a serial poll on the 3468A. Remember to check
the command structure for the controller you are using. The status byte returned
by the 3468A should indicate that bits O and 7 are true. Many controllers will
show a value of “129”. Looking at Figure 4-4 we can see that the value 129 is
equal to the sum of the decimal values of bits O and 7. Bit 7 is true because of
the power-on/reset that occurred. Bit O indicates that a measurement has been
made and data is ready. This step of the exercise simply serves to show that bits
in the status register may be true without causing the Service Request message to
be sent. Remember that when Service Request is sent, the SRO annunciator turns
on.
76