Model 7002Switch System Instruction Manual - Advanced Test ...

IEEE-488 ReferenceB6 is called the RQS bit. Serial polling causes bit B6 (RQS)to reset. Serial polling is discussed in more detail later in thisparagraph (see “Serial Poll and SRQ”).The following operations clears all bits of the Status ByteRegister:1. Cycling power.2. Sending the *CLS common command.NOTEThe MAV bit may or may not be cleared.Service Request Enable Register — This register is programmedby the user and serves as a mask for the StatusSummary Message bits (B2, B3, B4, B5 and B7) of the StatusByte Register. When masked, a set summary bit in theStatus Byte Register will not set bit B6 (MSS/RQS) of theStatus Byte Register. Conversely, when unmasked, a setsummary bit in the Status Byte Register will set bit B6.A Status Summary Message bit in the Status Byte Register ismasked when the corresponding bit in the Service RequestEnable Register is cleared (0). When the masked summarybit in the Status Byte Register sets, it is ANDed with the correspondingcleared bit in the Service Request Enable Register.The logic “0” output of the AND gate is applied to theinput of the OR gate and thus, will not set the MSS/RQS bitin the Status Byte Register.A Status Summary Message bit in the Status Byte Register isunmasked when the corresponding bit in the Service RequestEnable Register is set (1). When the unmasked summary bitin the Status Byte Register sets, it is ANDed with the correspondingset bit in the Service Request Enable Register. Thelogic “1” output of the AND gate is applied to the input ofthe OR gate and thus, will set the MSS/RQS bit in the StatusByte Register.The Service Request Enable Register can be read using thefollowing common query command (see paragraph 5.10.13for details):*SRE?The Service Request Enable Register is not cleared when itis read using the *SRE? query command. The Service RequestEnable Register will clear when power is cycled or aparameter (n) value of zero is sent with the *SRE command(*SRE 0).Serial poll and SRQAny enabled event summary bit that goes from 0 to 1 will setRQS and generate a service request (SRQ). The user’s testprogram can periodically read the Status Byte Register tocheck to see if a service request (SRQ) has occurred andwhat caused it. In the event of an SRQ, the program can, forexample, branch to an appropriate subroutine that will servicethe request. Typically, service requests (SRQs) are managedby the serial poll sequence of the Model 7002. If anSRQ does not occur, bit B6 (RQS) of the Status Byte Registerwill remain cleared and the program will simply proceednormally after the serial poll is performed. If an SRQ doesoccur, bit B6 of the Status Byte Register will set and the programcan branch to a service subroutine when the SRQ is detectedby the serial poll.The serial poll will automatically reset RQS of the StatusByte Register. This will allow subsequent serial polls tomonitor Bit 6 for an SRQ occurrence generated by otherevent types. After a serial poll, the same event can cause anotherSRQ, even if the event register which caused the firstSRQ has not been cleared.A serial poll clears RQS but does not clear MSS. The MSSbit will stay set until all Status Byte event summary bits arecleared or until the corresponding bits in the service requestenable registers are cleared.The individual bits of the Service Request Enable Registercan be set or cleared by using the following common command(see paragraph 5.10.12 for details):*SRE The following HP BASIC 4.0 programming example demonstrateshow serial poll can be used to detect an SRQ.10 REMOTE 70720 CLEAR 7075-23