User Manual

Status Reporting 33
Keysight InfiniiVision 1000 X-Series Oscilloscopes Programmer's Guide 755
Status Byte Register (STB)
The Status Byte Register is the summary-level register in the status reporting
structure. It contains summary bits that monitor activity in the other status
registers and queues. The Status Byte Register is a live register. That is, its
summary bits are set and cleared by the presence and absence of a summary bit
from other event registers or queues.
If the Status Byte Register is to be used with the Service Request Enable Register
to set bit 6 (RQS/MSS) and to generate an SRQ, at least one of the summary bits
must be enabled, then set. Also, event bits in all other status registers must be
specifically enabled to generate the summary bit that sets the associated
summary bit in the Status Byte Register.
The Status Byte Register can be read using either the *STB? Common Command
or the programming interface serial poll command. Both commands return the
decimal-weighted sum of all set bits in the register. The difference between the
two methods is that the serial poll command reads bit 6 as the Request Service
(RQS) bit and clears the bit which clears the SRQ interrupt. The *STB? command
reads bit 6 as the Master Summary Status (MSS) and does not clear the bit or have
any affect on the SRQ interrupt. The value returned is the total bit weights of all of
the bits that are set at the present time.
The use of bit 6 can be confusing. This bit was defined to cover all possible
computer interfaces, including a computer that could not do a serial poll. The
important point to remember is that, if you are using an SRQ interrupt to an
external computer, the serial poll command clears bit 6. Clearing bit 6 allows the
oscilloscope to generate another SRQ interrupt when another enabled event
occurs.
No other bits in the Status Byte Register are cleared by either the *STB? query or
the serial poll, except the Message Available bit (bit 4). If there are no other
messages in the Output Queue, bit 4 (MAV) can be cleared as a result of reading
the response to the *STB? command.
If bit 4 (weight = 16) and bit 5 (weight = 32) are set, the program prints the sum of
the two weights. Since these bits were not enabled to generate an SRQ, bit 6
(weight = 64) is not set.
The following example uses the *STB? query to read the contents of the
oscilloscope's Status Byte Register.
myScope.WriteString "*STB?"
varQueryResult = myScope.ReadNumber
MsgBox "Status Byte Register, Read: 0x" + Hex(varQueryResult)
The next program prints 0xD1 and clears bit 6 (RQS) and bit 4 (MAV) of the Status
Byte Register. The difference in the output value between this example and the
previous one is the value of bit 6 (weight = 64). Bit 6 is set when the first enabled
summary bit is set and is cleared when the Status Byte Register is read by the
serial poll command.