HP 3336A - Page 46

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Model 3336A/B/C
Status Byte is true, the -hp- 3336 requests service. If bit 0 is also true, the reason it requested
service is because the -hp- 3336 received a program string it could not recognize or respond
to. In this case, the appropriate action may be to print a message advising the operator that
the -hp- 3336 received an invalid instruction. Only the instrument status associated with bits
O thru 3 can cause service requests. See Masking Service Requests.
7654321 0 Status Byte Bits
FRFxSSSS F = Flag; R = Request Service; S = Status
1 = Program String Error
1 = Sweep Stopped
1 = Sweep Started
1 = System Failure (Main Oscillator Unlocked, Ext. Ref. Unlocked)
1 = Sweep Flag (Sweep in progress)
1 = Service Requested
1 = Busy Flag (3336 is busy processing data)
Does not cause a Request Service Message
3-143. Status Bytes are requested by the controller by conducting a Serial Poll (see
Paragraph 3-144, Serial Polling). Usually, a serial poll is conducted in response to a Require
Service Message received from an instrument on the HP-IB. Occasionally, a Serial Poll is
conducted even though a Require Service Message was not received. The programmer may
wish to check the status of an instrument function that is encoded in the Status Byte but does
not generate a Service Request. There are two and up to six such functions in the -hp- 3336.
Bit 0 through bit 3 of the Status Byte are maskable. That is, the corresponding conditions of
each bit will not cause a Service Request unless programmed to do so. Bit 7 of the Status
Byte is the Busy Flag. This bit will be true (1) when the -hp- 3336 is processing instructions
and is not capable of communicating, except for the Status Byte, over the HP-IB.
3-144. Serial Polling. A Serial Poll is a routine in the program that sequentially requests the
Status Byte from some or all devices on the HP-IB. The structure of the routine depends on
the way the controller implements the Serial Poll and the purpose of the poll. Some con-
trollers have a single program statement that enables a Serial Poll, polls the addressed device
and then disables the Serial Poll. In this case, a Serial Poll of a system consists of several
Serial Polls (one for each device). Recall'that Serial Polls are sometimes conducted on a
single device to learn the status of an instrument that is encoded in the Status Byte but does
not generate a Service Request.
3-145. Implementation. The syntax and mnemonics for the controller statements that im-
plement a Serial Poll are found in the controller documentation. The structure of the Serial
Poll (what instruments to be polled in what order) routine is developed in accord with the
total system. Only the listen addresses of the devices to be polled and the definitions of the
bits in the Status Byte are taken from the instrument documentation. The listen address of the
-hp- 3336 is $. A technical description of the Status Byte Message implementation is presented
in Figure 3-A-8 of Appendix A.
Operation
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