Status Byte Register (Stb) - Agilent Technologies InfiniiVision 7000A Series Programmer's Manual

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)
Agilent InfiniiVision 7000A Series Oscilloscopes Programmer's Guide
9
Status Reporting
757