Chapter 7
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BB6032-14
Photoacoustic Gas Monitor
LumaSense Technologies
1314i / 1412i / 1512i / 3434i
Page 79 of 81
7.1 Introduction to Service Requests
Under certain circumstances, it is necessary for the Monitor to demand
attention from the controller or otherwise interrupt the normal sequence of
the interface communication. The Monitor does this by raising the Service
Request (SRQ) line in the Status Byte. Service requests can, therefore, be
used for device synchronization. The SRQ function is commonly used to
synchronize the operation of the Monitor with an external computer that has
RS–232 controller capabilities. Typically, SRQ indicates that data is ready to
be transmitted or an error condition exists. The Monitor generates a Service
Request which interrupts the computer. The computer is then free to
perform other tasks while waiting for a signal from the Monitor.
Fig. 7.1
Logic diagram of the “Special Event” Event register, Event
Enable Register, Status Byte and Service Request Enable
Register.
Fig. 7.1 shows part of the logic diagram for generating Service Requests.
The input to 5 of the 8 bits of the Status Byte (bits 1 – 4 and 8) come from
the 5 pairs of Event Registers and Event Enable Registers (in this case the
“Special Event” Registers) is shown.
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The Event Enable Registers act as masks for the Event Registers.
•
The Service Request Enable Register acts as a mask for the Status
Byte.
