Parallel Interfaces for DAQ Systems

7/28/2019 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

Parallel Interfaces for DAQ Systems

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