Parallel Interfaces for DAQ Systems
Transcript of Parallel Interfaces for DAQ Systems
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GPIB tutorial(according to Agilent and National Instruments sources)
Jn aliga
Technical University of KoiceSlovak Republic
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Parallel interfaces in DAQ
GPIB (tutorial according to Agilentand National Instruments sources)
Parallel port
Non-standard interfaces (seelectures on multifunction plug-inboards)
System and computer busses PCI,VXI, ... (see lectures on plug-inboards)
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History
1965 Hewlett-Packard designsHP-IB forinstrumentation systems
1975 HP-IB becomes IEEE 488standard 1987 IEEE 488.2 adopted; IEEE 488-
1978 becomes IEEE 488.1-1987 1992 SCPI Specification introducedfor
IEEE 488 instruments 1990 IEEE 488.2 Standard revised 1993 National Instruments proposes
high-speed extensions to IEEE 488.1called HS488
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Basic characteristics
Any instrument can be used Each instruments (up to 15) has its unique
address within range 0-31 in basicaddressing mode
Linear or star cable configuration 24/25 wires 3 types of connectors (Amphenol CHAMP or
Cinch Series 57 MICRO RIBBON type)
Total length of cable 20m, max. 4m perinstrument
TTL levels, negative logic, drivers: 3-stateor open collector (NDAC, NRFD, SRQ)
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Types of GPIB messages
Communication is based on variousmessages:
Device-dependent messages related
(mainly) to the instrument measuringfunctions
Interface messages (commandmessages commands as some device
dependant messages accordingIEEE488.2) related to thecommunication (interface) functions
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Main communication functions
System Controller and Active Controller controls communication, send interfacemessages, e.g. monitors bus activities,addresses (enables) instruments, etc.
Listener receives the device -dependentmessages
Talker sends the device -dependentmessages
Simple system does not need controller the device work always in the modes talk-only and listen-only
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Interface Signals and Lines
Data bus (8 lines)similar to anycomputer data bus:commands/data
Handshaking lines =asynchronous controlof transfer on DIO
Interface management
lines = control ofsome interfacefunctions
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Handshaking (HS) lines
NRFD (Not Ready for Data) Acceptor of HS NDAC (Not Data Accepted) Acceptor of HS DAV (Data Valid) Source of HS
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Interface Management Lines ATN (Attention) - controller drives ATN true when
it uses the DIO to send commands, and falsewhen a Talker can send data messages.
EOI (end or identify) two purposes: Talker: to mark the end of a message string, Controller: to tell devices to identify their response in a
parallel poll. IFC (interface clear) The System Controller
drives the IFC line to initialize the bus andbecome CIC.
REN (remote enable) The System Controllerdrives the REN line to place devices in remote orlocal program mode.
SRQ (service request) Any device can drive theSRQ line to asynchronously request service fromthe Controller.
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IEEE 488.2 and SCPI
488.1 (1975) missing mainly: definitionof data formats, status reporting, messageexchange protocol, common configurationcommands, device-specific commands,etc.
488.2 (1987) arisen from 488.1(compatible), software oriented, increasesdata format compatibility, status reportingand error handling
SCPI device-specific commands comingfrom generalized instrument model
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Comparison of IEEE 488.1 488.2
and SCPI
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IEEE 488.2 Mandatory Controller Seq.Description Control Sequence
Send ATN-true commands SEND COMMAND
Set address to send data SEND SETUP
Send ATN-false data SEND DATA BYTES
Send a program message SEND
Set address to receive data RECEIVE SETUP
Receive ATN-false data RECEIVE RESPONSE MESSAGE
Receive a response message RECEIVE
Pulse IFC line SEND IFC
Place devices in DCAS DEVICE CLEAR
Place devices in local state ENABLE LOCAL CONTROLSPlace devices in remote state ENABLE REMOTE
Place dev. in remote with local lockout state SET RWLS
Place devices in local lockout state SEND LLO
Read IEEE 488.1 status byte READ STATUS BYTE
Send group execution trigger (GET) message TRIGGER
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IEEE 488.2 Controller Protocols
Keyword Name Compliance
RESET Reset System Mandatory
FINDRQS Find Device RequestingService
Optional
ALLSPOLL Serial Poll All Devices Mandatory
PASSCTL Pass Control Optional
REQUESTCTL Request Control Optional
FINDLSTN Find Listeners OptionalSETADD Set Address Optional, but requires
FINDLSTN
TESTSYS Self-Test System Optional
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IEEE 488.2 Instruments
Minimal set of interface capabilitiesof each device: To send and receive data (T5, T6, TE5,
TE6, L3, L4, LE3, LE4, AH1, SH1) To request service (SR1) To respond to a device clear (DC1)
+ other capabilities are optional:RL0/RL1; PP0/PP1; DT0/DT1; E1/E2;C0/C in some version.
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IEEE 488.2 Common Commands
Mnemonic Group Description*IDN? System Data Identification query
*RST Internal Operations Reset
*TST? Internal Operations Self-test query
*OPC Synchronization Operation complete
*OPC? Synchronization Operation complete query
*WAI Synchronization Wait to complete
*CLS Status and Event Clear status
*ESE Status and Event Event status enable
*ESE? Status and Event Event status enable query
*ESR? Status and Event Event status register query
*SRE Status and Event Service request enable
*SRE? Status and Event Service request enable query
*STB? Status and Event Read status byte query
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IEEE 488.2 Device Status Model
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SCPI Instrument Model
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Parallel port IEEE1284
Primary 8-bits interface forconnecting printers (Centronics)
1994 the first standard IEEE 1284:
Standard (centronics compatible)parallel port (SPP): one way data lines+ 3-wire handshaking + additionalstatus, control lines very simple:transfer fully controlled by software(microprocessor)
EPP ECP
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Enhanced parallel port
Bidirectional data lines
Similar to microcontroller buscommunication (addressing registersin printer and in PC, then datatransfer)
Transfer rate up to 10MB/s
Data transfer partially controlled byPC hardware
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Extended capabilities parallel port
Bidirectional data transfer fullysupported by PC hardware (data andaddress written to the register in PC
are automatically send to the printer Networking (daisy chain: input =
host and output =pass troughconnectors)
Parallel port is used for some low costDAQ devices