Option 05IEEE488 Interface

Title Page

8-1. Introduction 8-3

8-2. Theory of Operation 8-3

8-3. Functional Block Description 8-3

8-4. Detailed Circuit Description 8-3

8-5. Main Assembly Connectors 8-3

8-6. Address Decoding Circuit 8-3

8-7. Isolation Circuits 8-4

8-8. IEEE-488 Controller 8-4

8-9. IEEE-488 Transceivers/Connector 8-5

8-10. General Maintenance 8-8

8-11. Removing the IEEE-488 Interface Option 8-8

8-12. Installing the IEEE-488 Interface Option 8-9

8-13. Performance Testing 8-9

8-14. Troubleshooting 8-10

8-15. Power-up Problems 8-10

8-16. Communication Problems 8-10

8-17. Failure to Select IEEE-488 Interface Option 8-10

8-18. Failure to Handshake on IEEE-488 Bus 8-11

8-19. Failure to Enter Remote 8-11

8-20. Failure to Receive Multiple Character Commands 8-12

8-21. Failure to Transmit Query Responses 8-12

8-22. Failure to Generate an End or Identify (EOI) 8-12

8-23. Failure to Generate a Service Request (SRQ) 8-12

8-24. Schematic Diagram 8-12

8-25. List of Replaceable Parts 8-12

8-1. Introduction

The IEEE-488 Interface turns the Fluke 45 into a fully programmable instrument for use with the IEEE Standard 488.1 (1987) interface bus (IEEE-488 bus). With the IEEE-488 Interface, the Fluke 45 can become part of an automated instrumentation system.

8-2. Theory of Operation

8-3. Functional Block Description

The IEEE-488 Assembly (A5) requires power supply voltages, address, data and control signals from the Fluke 45 Main Assembly (A1) to operate. The A5 assembly implements the circuitry necessary to satisfy the IEEE-488.1 standard for programmable instrumentation.

8-4. Detailed Circuit Description

The IEEE-488 Assembly comprises the following functional blocks: the Main Assembly Connectors, the Address Decoding Circuit, the Isolation Circuits, the IEEE-488 Controller, and the IEEE-488 Transceivers and Connector. These five blocks are described in the following paragraphs. Signal names mentioned during this discussion are:

ACON*AC line power on IRQ2*IEEE-488 interrupt request OPSIEEE-488 option sense

OPTSW* IEEE-488 option power switch control signal

8-5. Main Assembly Connectors

The IEEE-488 Assembly interfaces with the Main Assembly through two ribbon cables that mount to the 14-position and 20-position connectors on each assembly. The 20-pin connector (A5J2) routes the 16-bit address bus from the Microprocessor (A1U6) to the circuitry on the IEEE-488 Assembly. The 14-position connector (A5J3) passes the eight-bit data bus and memory control signals between the two assemblies.

The IEEE-488 Assembly is powered by the +5.2V dc power supply (VCC) from the Main Assembly. VCC is connected to the IEEE-488 Assembly via A5J3-1. The logic common return (GND) is through A5J2-20.

8-6. Address Decoding Circuit

When a memory read or memory write cycle intended for the IEEE-488 Controller (A5U6) is in progress, the 13 address bits ADD(15) through ADD(3) from A1U6 are decoded by A5U1, A5U2, and A5U5 to generate an active low chip-select signal. The chip-select signal (A5U5-8) goes low when two events occur: OPTSW* (A5J3-12) is near -5.2V dc (VEE), and the address bus indicates that the Microprocessor is accessing memory between addresses 0028 and 002F hexadecimal (inclusive). When the Fluke 45 is operating on battery power, the Microprocessor turns off the power to the IEEE-488 Assembly by driving the OPTSW* signal (A5J3-12) to VCC. This signal drives A5U1-6 to about +4.3V dc (through A5CR1), disabling the Address Decoding Circuit.

8-7. Isolation Circuits

The Isolation Circuits allow the Microprocessor to turn off power to the A5U6, A5U7, and A5U8 components. These three components consume the majority of the power on the IEEE-488 Assembly; normal meter operation on batteries is extended by approximately 100% with this power isolation scheme.

The Microprocessor determines that the IEEE-488 Assembly is installed in the meter by checking the state of the OPS signal (A5J2-18). This signal is pulled up to VCC by resistor A1R39 and is shorted to logic ground on the IEEE-488 Assembly. If A1U6-29 is low, the Microprocessor assumes that the IEEE-488 Assembly is installed. If the ACON* signal (A1U6-33) is low (indicating operation on ac power), the Microprocessor drives A1U6-28 high. As a result, the OPTSW* signal (A1U7-3) is driven to VEE, and transistor A5Q1 turns on. This transistor passes current from the VCC power supply to the VCC2 power supply to bias A5U6, A5U7, and A5U8. Normally VCC2 is approximately 0.1V less than VCC.

When OPTSW* (A5J3-12) is near VCC (battery operation), diode A5CR1 and pulldown resistor A5R1 cause the non-inverting octal tri-state buffer (A5U4) to be tri-stated off by holding inputs A5U4-1 and A5U4-19 near VCC. This octal buffer isolates six Microprocessor outputs (ADD(2), ADD(1), ADD(0), WR*, RD, and E clock) from the IEEE-488 Controller (A5U6) when the meter is operating on batteries. A5U4 also buffers the chip-select signal (A5U5-8) that goes to A5U6 and the interrupt output signal from A5U6-10.

The eight bit data bus from the Microprocessor is isolated from A5U6 by an octal bus transceiver with tri-state outputs (A5U3). This transceiver is enabled only when the Address Decoding Circuit detects that a memory cycle for the IEEE-488 Assembly is in progress and A5U3-19 is driven low. If the memory cycle is a read cycle, the R/W* signal (A5U3-1) is high and the transceiver buffers the eight bit data from A5U6 to A1U6. If the memory cycle is a write cycle, the R/W* signal (A5U3-1) is low and the transceiver buffers the eight-bit data from A1U6 to A5U6.

8-8. IEEE-488 Controller

The IEEE-488 Controller (A5U6) is an integrated circuit that performs the transfer of information between the IEEE-488 standard bus and the Microprocessor. Once it has been programmed by the Microprocessor via the eight register microprocessor interface, A5U6 performs IEEE-488 bus transactions independently until it must interrupt the Microprocessor for additional information or data.

The IEEE-488 Controller is clocked by a 921.6-kHz square-wave clock. This clock (A5U4-5) is generated by buffering the E clock (A5U4-15) from the Microprocessor. The IEEE-488 Controller uses this clock to run the internal state machines that handle IEEE-488 bus transactions.

The IEEE-488 Controller can be given a hardware reset with either of the following two methods:

• If the system reset signal RESET (A5J3-14) goes high or if OPTSW* (A5J3-12) goes high, then NOR gate output A5U2-10 goes low, and the D flip-flop Q output A5U9-9 goes low. This flip-flop output drives the reset input (A5U6-22), forcing the IEEE-488 Controller into its reset state.

• When the meter is initially powered up, both RESET and OPTSW* are high, forcing the IEEE-488 Controller reset input (A5U6-22) to be low. As long as OPTSW* is high, VCC2 is near ground and A5U6 is not biased, so A5U6-22 is held low to avoid sourcing current into A5U6-22 while A5U6 is unbiased.

When the Microprocessor drives OPTSW* to VEE to enable the VCC2 power supply, the CLR* input to the D flip-flop (A5U9-13) goes high to enable the flip-flop. The Q output (A5U9-9) remains low until the Microprocessor does an initial dummy memory cycle to the IEEE-488 Controller (approximately 1 ms later.) The rising edge at the end of the chip select signal (A5U9-11) clocks the flip-flop and causes the Q output to go high. This action removes the hardware reset to the IEEE-488 Controller. This delay is followed by another dummy read cycle and a series of six memory write cycles that program the IEEE-488 Controller.

For each character that it receives or transmits, the IEEE-488 Controller generates an interrupt to the Microprocessor. These interrupts are generated by driving the open-drain interrupt output A5U6-10 low. This signal is buffered by a tri-state buffer whose output at A5U4-3 drives the IRQ2* input to the Microprocessor low. When the Microprocessor responds to the interrupt and takes the necessary actions by reading and writing registers in the IEEE-488 Controller, both A5U6-10 and, subsequently, A5U4-3 go high again. Resistor A5R3 provides a pull-up termination on open-drain interrupt output A5U6-10. Tri-state buffer output A5U4-3 is pulled up by resistor A5R2 to terminate the IRQ2* signal when the buffer is tri-stated off.

When the Microprocessor performs a memory cycle to the IEEE-488 Controller, the lower three bits of the address bus that are buffered by A5U4 (ADD(2) through ADD(0)) select the register being accessed in A5U6. When a memory read cycle is performed, chip-enable A5U6-3 goes low, and A5U6-5 (DBIN) goes high. These actions enable A5U6, driving the contents of the selected register onto the data bus and through the data bus transceiver to the Microprocessor. When a memory write cycle is performed, chip-enable A5U6-3 goes low, and A5U6-4 (WE*) goes first low and then high to latch the data being driven from the Microprocessor (through A5U3) into the IEEE-488 Controller.

The IEEE-488 Controller interfaces to the IEEE-488 Transceivers using an eight-bit data bus, eight interface signals, and two transceiver control signals (A5U6-33 and A5U6-24).

The controller-in-charge signal (A5U6-33), which should always be high, controls the direction of the SRQ, ATN, IFC, and REN IEEE-488 transceivers in A5U8.

The talk enable output (A5U6-24) is either low when the IEEE-488 Controller is not addressed to talk or high when the controller is addressed to talk. This signal determines the direction of all IEEE-488 Transceivers except SRQ, ATN, IFC, and REN.

8-9. IEEE-488 Transceivers/Connector

The IEEE-488 Transceivers (A5U7 and A5U8) are octal transceivers that are specifically designed to exhibit the proper electrical drive characteristics to meet the IEEE-488 standard. These transceivers are configured to match the control signals available on the IEEE-488 Controller. Assuming that A5U6-33 is always high, Table 8-1 describes the transceiver direction control. The IEEE-488 Transceivers connect to a 24-position connector, which mates with the ribbon cable leading to the IEEE-488 connector mounted at the rear of the meter chassis.

Table 8-1. IEEE-488 Transceiver Control

Transceiver

TE = 0 (Listener)

TE = 1 (Talker)

DI01..DI08

Receiver

Transmitter

SRQ

Transmitter

Transmitter

ATN

Receiver

Receiver

EOI

Receiver

Receiver (ATN = 0)

Receiver

Transmitter (ATN = 1)

DAV

Receiver

Transmitter

NRFD

Transmitter

Receiver

NDAC

Transmitter

Receiver

IFC

Receiver

Receiver

REN

Receiver

Receiver

Figure 8-1. Disassembly

24 LINE CABLE ASSEMBLY RETAINING SCREWS

qb41c.epc

Figure 8-2. IEEE-488 Interface Connector

24 LINE CABLE ASSEMBLY RETAINING SCREWS

#6 - 32 x 1/2" PANHEAD SCREW

qb42c.eps

Figure 8-3. IEEE-488 Module Assembly

8-10. General Maintenance

8-11. Removing the IEEE-488 Interface Option

The following instructions can be used for access and servicing an IEEE-488 Interface

Option that is already installed in a Fluke 45 Dual Display Multimeter. For initial installation, refer to the Instruction Sheet (PN 856005) provided with the option.

1. Make sure the meter is turned off and unplugged from the power outlet.

2. Remove the screw on the bottom of the meter case and the two screws from the rear bezel (as shown in Figure 8-1A). While holding the front panel, slide the case and rear bezel off the chassis (see Figure 8-1B). (At this point, the rear bezel is not secured to the case.)

3. Using needle nose pliers, disconnect the 24-line cable assembly at the IEEE-488 PCA by alternately pulling up on each end of its connector. See Figure 8-2.

4. Refer to Figure 8-3 for the remaining steps. Remove the panhead Phillips screw at the rear of the IEEE-488 PCA.

5. Using needle nose pliers, detach the two ribbon cables at the front part of the IEEE-488 PCA. Alternately pull up on each end of the cable connectors.

6. Remove the IEEE-488 PCA, disengaging the assembly from both the small slot in the side of the meter and the plastic standoff at the front corner of the assembly.

8-12. Installing the IEEE-488 Interface Option

Use the following procedure to install the IEEE-488 Interface Option.

1. Turn the meter off, and unplug the power connection.

2. Check that the plastic standoff remains in the appropriate hole in the meter PCA (narrow end of the standoff down; see Figure 8-3).

3. If necessary, install the two ribbon cables on the IEEE-488 PCA. Each cable fits in only one socket and in only one direction. Make sure the cables lock firmly in place.

4. Attach opposite ends of the ribbon cables onto the Fluke 45 Main PCA.

5. Install the IEEE-488 PCA in the Fluke 45 with the dual ribbon cables facing the front of the meter. The IEEE-488 PCA slips into the small slot in the side of the meter. The end of the plastic standoff fits into the hole in the IEEE-488 PCA. Make sure the IEEE-488 PCA is firmly gripped against the retainer on the standoff. The rear of the IEEE-488 PCA should rest upon the support just forward of the transformer.

6. Secure the rear of the IEEE-488 PCA with the panhead Phillips screw.

7. Connect the 24-line cable assembly to the IEEE-488 PCA. (See Figure 8-2.)

8. Reinstall the meter case so it seats properly in the front panel. Attach the rear bezel with the two panhead Phillips screws, and secure the case with the flathead Phillips screw in the bottom.

8-13. Performance Testing

Use the performance test program in Figure 8-1 to verify operation of the IEEE-488 Interface. This program is written for use with the Fluke 182A Instrument Controller and its interpreted BASIC language. The program may be adapted to the language of any IEEE-488 controller.

This performance test communicates to a meter that has been configured for IEEE-488 operation at address 0. Lines 160 and 170 initialize the IEEE-488 bus and send a selective device clear to the meter. A multiple byte command is sent to the meter (by line 190) to clear the meter status. Another command sequence (including a query) is sent to the meter by line 210; the meter asserts Service Request (SRQ) to signal that a response is available. Lines 530 through 560 first poll the meter for status, then input the response from the meter. Lines 230 through 270 test for proper operation and print the results.

140

IA% = 0%

! instrument IEEE address

150

S% = -1%

! initialize spl response

160

TERM

! terminate input only on EOI

170

INIT PORT 0

! initialize IEEE-488 bus

180

CLEAR @IA%

! selective device clear

190

PRINT @IA%,"*cls"

! clear instrument status

200

ON SRQ GOTO 53 0

! enable SRQ interrupt

210

PRINT @IA%,"*cls;*sre 16;*idn?"

! SRQ on Message Available

220

WAIT 500% FOR SRQ

! allow time to execute commands

230

IF S% >= 0% THEN 260

240

PRINT "Instrument failed to generate a Service Request"

250

STOP

260

PRINT "Serial Poll =";S%;"(should

be 80)."

270

PRINT "Identification Query Response = ";R$

280

STOP

500

!

510

! Service Request interrupt

520

!

530

S% = SPL(IA%)

! get instrument serial poll status

540

IF S% AND 16% THEN 550 ELSE 560

550

INPUT LINE @IA%,R$

! if MAV set get the response

560

RESUME 230

! end of SRQ interrupt

999

END

Figure 8-4. IEEE-488 Interface Performance Test

Figure 8-4. IEEE-488 Interface Performance Test

8-14. Troubleshooting

8-15. Power-up Problems

The following discussion identifies probable fault areas if the installation of an IEEE-488 Interface Option causes power-up failure for the Fluke 45. The problem is probably a short on A5P2 or A5P3; the Microprocessor on the Main Assembly is prevented from accessing ROM and RAM correctly. Two extender cables are available (PN 867952 and 867957) to assist during troubleshooting.

• The first thing to check is whether GND is shorted to either VCC or VCC2 on the IEEE Assembly.

• The short may also be an interface signal to either VCC, GND, or another interface signal. The logical signals to check are DATA(7..0), ADD(15..0), RD*, WR*, E, and RESET*.

• The short may be due to a CMOS input that has been damaged from static discharge; the short is then detectable only when the circuit is powered up. Use an oscilloscope to check activity on each of the interface signals. Verify that signals are able to transition normally between 0 and 5V.

8-16. Communication Problems

8-17. Failure to Select IEEE-488 Interface Option

IEEE-488 Interface selection procedures are described in Chapter 3.

If the IEEE-488 Interface Option is not detected by Fluke 45 software, there may be a problem with the OPS or ACON* signal. The IEEE Interface Option grounds the OPS signal (A5P2-18), which is normally pulled up to VCC on the Fluke 45 Main Assembly. The Microprocessor determines that the IEEE-488 Interface Option is not installed if OPS (A1U6-29) is detected high.

Further, software does not allow the IEEE-488 Interface Option to be selected if the ACON* signal is detected high. Since ACON* is high when the meter is operating on battery power, the IEEE-488 Interface Option cannot be selected as the active interface during battery operation. The displayed "IEEE" message is dim, and the battery indicator blinks if the Fluke 45 software detects ACON* to be high when the option editor is entered. The ACON* signal (A1U6-33) is low when the meter is operating from line power.

8-18. Failure to Handshake on IEEE-488 Bus

Check VCC2 with a voltmeter. When the Fluke 45 is operating on line power, VCC2 should be about 0.1V lower than VCC. VCC2 is controlled by the Microprocessor, which sets A1U6-28 high when operating on line power and causes OPTSW* to be driven to a -5.0V dc level. The OPTSW* signal controls the gate of FET switch A5Q1 on the IEEE-488 Interface Option to turn VCC2 on.

The Reset circuit consists of A5CR1, A5R1, A5U2, and A5U9. When the meter is operating on batteries, the Reset circuit converts the OPTSW* signal to a digital signal that disables access to A5U6. When operating from batteries, OPTSW* is at about 5.0V dc, A5U2-9 is high, A5U2-10 is low, and A5U9-9 is low to reset A5U6 via pin 22.

When the meter is connected to ac line voltage again, this circuit resets A5U6. OPTSW* transitions to -5.0V dc, A5U2-9 is low (near GND), A5U2-10 is high, and A5U9-9 stays low until the Address Decoder detects a memory access to the IEEE-488 Interface Option. About 1.0 ms after OPTSW* goes to -5.0V dc, the initial read access clocks A5U9-11, causing A5U9-9 to go high to remove the reset from A5U6-22. This action is followed by another "dummy" read cycle for delay. The Main Assembly then sends six write cycles to initialize A5U6. The IRQ2 interrupt is then enabled, and the serial poll status byte is initialized. At this point, the IEEE-488 Interface Option is ready to respond to transactions on the IEEE-488 bus.

Note

Each time that the IEEE Interface Option is selected in the BAUD menu (by pressing [AUTO]), the IEEE-488 Interface Option initialization is repeated as described above, with the exception that no hardware reset is performed via the OPTSW* signal.

8-19. Failure to Enter Remote

If the IEEE-488 Interface Option does not enter remote, check that the remote/local control circuit is operating properly. When the IEEE-488 Interface Option is the active instrument interface, the remote/local control state is polled by the Main PCA approximately every 1.0 ms. Normally, A5U5-8 goes low for approximately 1.0 ^s during the read cycle that checks the state of A5U6. If A5U3-11 is low during the read cycle, A5U6 is in the local state. If A5U3-11 is high during the read cycle, A5U6 is in the remote state. When A5U6 indicates that it is in remote, the REMOTE indicator on the display is turned on.

8-20. Failure to Receive Multiple Character Commands

Monitor the interrupt signal from A5U6-10 during attempts to communicate with the meter. Each byte received with the ATN signal (A5U6-31) high should cause the interrupt signal to go low. Follow the interrupt signal through A5U4, and verify that it arrives at A5J3 properly. If the interrupt is not detected by A1U6, it will remain low indefinitely. A5U6-10 will only go high when both the interrupt is detected and the received byte is removed from A5U6 by A1U6.

8-21. Failure to Transmit Query Responses

Check that TE (A5U6-24) goes high when the interface is addressed to talk. This signal must go high to allow the bus interface transceivers to change the direction of DIO1 through DIO8, EOI, DAV, NRFD, and NDAC. Verify that each of these signals passes through A5U7 and A5U8 properly.

8-22. Failure to Generate an End or Identify (EOI)

When the IEEE-488 Interface Option sends the Line Feed termination character with a message, the EOI signal should also be set true. When EOI is true, A5U6-30 should go low. Follow this signal from A5J1 through A5U8 to A5U6.

8-23. Failure to Generate a Service Request (SRQ)

When a Service Request is being generated, A5U6-32 should be low. Follow this signal through A5U8 to connector A5J1. When a Serial Poll (SPL) is performed by the IEEE-488 bus controller, A5U6-32 will go high again.

Note

If the meter is in the remote state without front panel lockout (i.e., REMS), a service request can be sent from the front panel by pressing [UPB].

8-24. Schematic Diagram

The schematic diagram for the IEEE-488 Interface Option is included in Chapter 9 of this manual.

8-25. List of Replaceable Parts

Figures 8-4 and 8-5 provide illustration for the parts lists in Tables 8-3 and 8-4, respectively. Refer to Chapter 6 for parts ordering information.

Table 8-2. Option -05 IEEE-488 Interface Final Assembly

Reference Designator

Description

Fluke Stock No.

Total Qty.

Note

A

5

IEEE-488 INTERFACE PCA

814152

1

H

1

SCREW,PH,P,LOCK,STL,6-32,.250

152140

1

H

2

CONN ACC,MICRO-RIBBON,SCREW LOCK KIT

836585

1

MP

1

SPACER,SNAP,PWB,NYL,1.375

845347

1

TM

1

PRINT MATL,INST SHT,FLUKE 45/IEEE-488

856005

1

W

7

CABLE ASSY,IEEE

834978

1

W

8

CABLE ASSY,FLAT,14 COND,MICROMOD,3 IN

831560

1

W

9

CABLE ASSY,FLAT,20 COND,MICROMOD,3 IN

831578

1

qb43c.eps

Figure 8-5. Option -05 IEEE-488 Interface Final Assembly qb43c.eps

Figure 8-5. Option -05 IEEE-488 Interface Final Assembly

Table 8-3. A5 IEEE-488 Interface PCA

Reference Designator

Description

Fluke Stock No.

Total Qty.

Note

C

6- 11

CAP,CER,0.1UF,±10%,25V,X7R,1206

747287

6

C

12

CAP,CER,0.022UF,±10%,50V,X7R,1206

747279

1

CR

1

* DIODE,SI,BV=75V,IO=250MA,SOT23

830489

1

J

1

HEADER,2 ROW,.100CTR,24 PIN

831834

1

J

2

HEADER,1 ROW,.050CTR,20 PIN

831529

1

J

3

HEADER,1 ROW,.050CTR,14 PIN

831511

1

Q

1

* TRANSISTOR,SI,PMOS,1W,D-PAK

836544

1

R

1,3

* RES,CERM,5.1K,±5%,125W,200PPM,1206

746560

R

2

* RES,CERM,47K,±5%,.125W,200PPM,1206

746685

1

R

4

* RES,CERM,220,±5%,.125W,200PPM,1206

746347

1

U

1,2

* IC,CMOS,QUAD INPUT NOR GATE,SOIC

830711

U

3

* IC,CMOS,OCTAL BUS TRANSCEIVER,SOIC

742577

1

U

4

* IC,CMOS,OCTL LINE DRVR,SOIC

801043

1

U

5

* IC,CMOS,8 INPUT NAND GATE,SOIC

830729

1

U

6

* IC,NMOS,GPIB CONTROLLER,PLCC

887190

1

U

7

* IC,LSTTL,OCTAL GPIB XCVR,SOIC

831651

1

U

8

* IC,LSTTL,OCTAL GPIB XCVR,SOIC

831669

1

U

9

* IC,CMOS,DUAL D F/F,+EDG TRG,SOIC

782995

1

Complete Circuit Diagram Receiver Pca

Figure 8-6. A5 IEEE-488 Interface PCA

qb44c.eps

Figure 8-6. A5 IEEE-488 Interface PCA

qb44c.eps

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