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15.5
GPIB Parallel Poll (PRE)
Complete Parallel Poll capabilities are offered by this instrument as defined in IEEE Std. 488.1. The
Parallel Poll Enable Register (which is set by the *PRE
<NRF>
command and read by the *PRE?
query) specifies which bits in the Status Byte Register are to be used to form the
ist
local message.
If any bit is ‘1’ in both the STB and the PRE then
ist
is ‘1’, otherwise it is ‘0’. The state of the
ist
message can also be read directly by the *IST? query.
The physical layer protocol of the Parallel Poll (determining which data line is to be driven and its
logic sense) is configured by the PPC and PPE commands and released by the PPU and PPD
commands in the manner defined by the standard. The instrument implements passive pull-up on
the DIO lines during Parallel Poll.
15.6
Query Error Register - GPIB IEEE Std. 488.2 Error Handling
These errors are much more likely to occur on the semi-duplex GPIB interface, which requires the
instrument to hold a response until addressed to talk by the controller. All the other interfaces
provide full duplex communication, with buffering in the physical layer which will usually hold a
response from the instrument until the controlling software reads it; there is no equivalent of the
GPIB state ‘addressed to talk’, so the instrument is not aware of the actions of the controller
The IEEE 488.2
UNTERMINATED
error arises if the instrument is addressed to talk and has nothing to
say, because the response formatter is inactive and the input queue is empty. This will cause the
Query Error bit to be set in the Standard Event Status Register, a value of 3 to be placed in the
Query Error Register and the parser to be reset.
The IEEE 488.2
DEADLOCK
error arises if the response formatter is waiting to send a response
message and the input queue becomes full. This will cause the Query Error bit to be set in the
Standard Event Status Register, a value of 2 to be placed in the Query Error Register and the
response formatter to be reset, discarding the waiting response message. The parser will then start
parsing the next
<PROGRAM MESSAGE UNIT>
from the input queue.
The IEEE 488.2
INTERRUPTED
error arises if the response formatter is waiting to send a response
message and a
<PROGRAM MESSAGE TERMINATOR>
has been read by the parser, or the input queue
contains more than one END message. This will cause the Query Error bit to be set in the Standard
Event Status Register, a value of 1 to be placed in the Query Error Register and the response
formatter to be reset, discarding the waiting response message. The parser will then start parsing
the next
<PROGRAM MESSAGE UNIT>
from the input queue.
15.7
Power on Settings
The following instrument status values are set at power on:
ITE
Input Trip Enable Register
= 0
EER
Execution Error Register
= 0
ESR
Standard Event Status Register
= 128 (pon bit set)
QER
Query Error Register †
= 0
ESE
Standard Event Status Enable Register †
= 0
STB
Status Byte Register
= 0
SRE
Service Request Enable Register †
= 0
PRE
Parallel Poll Response Enable Register †
= 0
†
Registers marked thus are normally only used through the GPIB
interface.
The Input Trip (ITR) Register will report any conditions which presently apply.
The instrument will be in local state with the keyboard active. The instrument parameters at power
on are the same as at the last switch off.
