Keithley 1793 User manual

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KEITH LEY
INSTRUCTION MANUAL
Model 1793/6423
IEEE Standard 488 Output
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Keithley Instruments, Inc.
28775 Aurora Road/Cleveland, Ohio 44139/(216] 248-0400/Telex: 98-5469
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WARRANTY
We warrant each of our products to be free from defects in material
and workmanship. Our obligation under this warranty is to repair
or replace any instrument or part thereof which, within a year after
shipment, proves defective upon examination. We will pay local
domestic surface freight costs.
To exercise this warranty, write or call your local Keithley repre
sentative, or contact Keithley headquarters in Cleveland, Ohio.
You will be given prompt assistance and shipping instructions.
REPAIRS AND
CALIBRATION
Keithley Instruments maintains a complete repair and calibration
service as well as a standards laboratory in Cleveland, Ohio.
A Keithley service faciiity at our Munich, Germany office is
available for our customers throughout Europe. Service in the
United Kingdom can be handled at our office in Reading. Addition
ally, Keithley representatives in most countries maintain service
and calibration facilities.
To insure prompt repair or recalibration service, please contact
your local field representative or Keithley headquarters directly
before returning the instrument. Estimates for repairs, normal
recalibrations and calibrations traceable to the National Bureau of
Standards are available upon request.
KEITHLEY
Keithley Instruments, lnc./28775 Aurora Road/Cleveland, Ohio 44139/U.S.A./[phone]/Telex: 98-5469
Keithley Instruments GmbH/Heiglhofstrasse 5/D-8000 Munchen 70/WEST GERMANY/1089) 714-40-65/Telex: 521 21 60
Keithley Instruments, Ltd./I, Boulton Road/GB-Reading, Berkshire RG2 ONL/GREAT BRITAIN/(0734) 86 12 87/Telex: 847047
Keithley Instruments SARL/2 Bis, Rue Ldon Blum/B.P. 60/91121 Palaiseau Cedex/FRANCE/(6) 011.51.55/Telex: 600933F
Keithley Instruments B.V./Leidsestraatweg 149/Postbus 1190 /NL-Woerden/NETHERLANDS/103480) 13 643/Telex: 40 311
Keithley Instruments SA/Filiale DUbendorf/Kriesbachstr. 4/CH-8600 Dubendorf/SWITZERLAND/01 821 94 44/Telex: 57 536
Keithley Instruments Handels-Gesellschaft m.b.H./DOblinger Hauptstr. 32/A-1190 Wien /AUSTRIA/0222 314 289/Telex: 13 45 00

INSTRUCTION I^IMUAL
MODEL 1793/64;^3
IEEE STANDARD 488 OUTPUT
COPYRIGHT 1979 KEITHLEY INSTRUMENTS, INC.
THIRD PRINTING, l^RCH 1981, CLEVELAND, OHIO U.S.A.
DOCUMENT NO. 30535, REV. 8

CONTENTS
SECTION
PAGE
1. GENERAL INFORMATION
1-1. INTRODUCTION
1-3. COMPATIBILITY
1-6. WARRANTY INFORMATION
1-8. CHANGE NOTICES
1-10. SAFETY SYMBOLS
1-12. SPECIFICATIONS
2. INITIAL PREPARATION
2-1. INTRODUCTION
2-3. UNPACKING AND INSPECTION
2-5. MODEL 1793 INSTALLATION
2-7. MODEL 6423 INSTALLATION
2-9. MODEL 1793/6423 OUTPUT CONNECTOR
3. OPERATION
3-1. INTRODUCTION
3-3. OPERATING INSTRUCTIONS
4. THEORY OF OPERATION
4-1. INTRODUCTION
4-4. POWER SUPPLY
4-6. PARALLEL TO SERIAL CONVERSION
4-12. SERIAL TO PARALLEL CONVERSION
4-14. BUS OPERATION
4-16. ADDRESS ACCEPTANCE
4-18. DATA SENDING
5. MAINTENANCE
5-1. INTRODUCTION
5-3. TEST POINT DATA
5-5. 1793/6423 VERIFICATION PROCEDURE
5-7. ADDRESSABLE MODE VERIFICATION
5-8. TALK ONLY MODE VERIFICATION
5-9. SPECIAL HANDLING OF STATIC SENSITIVE DEVICES
6. REPLACEABLE PARTS
6-1. GENERAL
6-3. ORDERING INFORMATION
6-5. SCHEMATIC
6-7. COMPONENT LAYOUTS
1-1
1-1
1-1
1-1
1-1
1-1
1-1
2-1
2-1
2-1
2-1
2-2
2-2
3-1
3-1
3-1
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-3
5-1
5-1
5-1
5-1
5-1
5-1
5-2
6-1
6-1
6-1
6-1
6-1
ILLUSTRATIONS
Figure 2-1.
Figure 2-2.
Figure 3-1.
Figure 4-1.
Figure 4-2.
Figure 5-1.
Installation of Model 1793,
Installation of Model 6423,
Switch 502
1793/6423 Flow Diagram. . .
Timing Diagram
Isolated Serial Data. .. ,
PAGE
2-3
2-4
3-2
4-2
4-3
5-1
11

MODEL 1793/6423
GENERAL INFORMATION
SECTION 1. GENERAL INFORMATION
1-1. INTRODUCTION.
1-2. The Model 1793/6423 is an IEEE Standard
488-1978 Bus Interface option that provides the
logic and control functions necessary to interface
the Keithley Models 177, 179 and 179-20A Digital
Multimeters, the Model 480 Picoammeter, and the
Model 642 Electrometer. It may be either field or
factory installed. The combination of the Model
1793/6423 and its host DMM, Picoammeter or Elec
trometer can operate in either the TALK ONLY or
ADDRESSABLE mode, as determined by the setting of an
internal switch. In the TALK ONLY mode, it can send
data to an IEEE compatible listener at one of seven
switch selectable rates, from 2.5 readings/second to
1 reading/hour. In the ADDRESSABLE mode, readings
may be triggered or non-triggered, depending on
whether its odd or even address is received from the
IEEE controller. The internal switch settings
determine the reading rate for the TALK ONLY mode,
and its address when in the ADDRESSABLE mode. The
Model 1793/6423 provides an output of 4-1/2 digit
ASCII data, sign, and overrange.
1-3. COMPATIBILITY.
1-4. The Model 1793 is compatible with the
following Keithley instruments:
a) Model 177 DMM Serial Number 16500 and above.
b) Models 179 and 179-2GA DMM Serial Number 24000
and above.
c) Model 480 Picoammeter Serial Number 12000 and
above. NOTE: The first 3-1/2 digits of the output
are the same as the 480 display.
1-5. The Model 6423 is compatible with the Model
642 Electrometer Serial Number 53402 and above.
1-6. WARRANTY INFORMATION.
1-7. The Warranty is given on the inside front
cover of this Instruction Manual. If there is a
need to exercise the warranty, contact the Keithley
Representative in your area to determine the proper
action to be taken. Keithley maintains service
facilities in the United Kingdom and West Germany,
as well as in the United States. Check the inside
front cover of this Manual for addresses.
1-8. CHANGE NOTICES.
1-9. Improvements or changes to the equipment which
occur after printing of the Instruction Manual will
be explained on a Change Notice sheet attached to
the inside back cover.
1-10. SAFETY SYMBOLS.
1-11. Safety symbols used in this manual are as
follows:
A
IMPORTANT
The /' \ symbol may be found in various places
in this manual. Carefully read the associated
CAUTION statements with regard to proper use and
handling of the equipment. Damage to the equip
ment may occur if these precautions are ignored.
\
This ^ symbol may be found in various places
in this manual. This symbol indicates those
areas on the equipment which are potential shock
hazards. Carefully read the associated WARNING
statements with regard to proper use and
handling of the equipment. Serious personal
injury may result if these precautions are
i gnored.
1-12. SPECIFICATIONS.
1-13. Detailed specifications for the Model 1793/
6423 are listed in Table 1-2. These specifications
are defined as the performance standards or limits
against which the Model 1793/6423 is tested. Table
1-1 lists general operating characteristics of the
Model 1793/6423. These characteristics are not
specifications, but are typical operating charac
teristics or constraints which are included as
additional information for the user.
TABLE 1-1
General Operating Characteristics
1. The 1793/6423 digital output low (pins 12 and 18
thru 24 on J501) is intended to be connected to a
ground point within 30VRMS of earth ground.
2. Common mode input to the meter shall not exceed
lO^V'Hz to guarantee valid data output.
3. 488 BUS outputs are open collector with Power
Up/Power Down protection (No invalid information
transmitted to the BUS).
4. Maximum transfer rate for one entire reading
(after being addressed) is 1msec.
1-1

GENERAL INFORMATION
MODEL 1793/6423
TABLE 1-2
Specifications, Model 1793/6423 IEEE-488 Output
OUTPUT:
DATA FORMAT:
4-1/2 digit ASCII data, sign, and overrange.
.XXXXX. ^CR LF,
'
Sign
(Plus implied)
Displ ay
Termi nator
T
OVERRANGE OUTPUT: ASCII "OVER" in place of "XXXXX"
LOGIC LEVELS: Meets all IEEE Std. 488-1978 specifications.
MODES OF OPERATION: (Selected by internal switches)
TALK ONLY: Allows user to connect meter to an IEEE-compatible
listener. Data outputted at seven switch
selectable rates from 2.5 rdgs/sec to 1 rdg/hr.
ADDRESSABLE: Allows user to connect meter to an IEEE-compatible
controller. Address selected by internal switches.
Non-Triggered addresses are even from 0 to 28.
Triggered address is non-triggered address +1.
NON-TRIGGER: Upon receiving its non-trigger address, outputs the
displayed reading
TRIGGER: Upon receiving its trigger address, initiates a
single A-D conversion and outputs the reading 400
msec later.
ISOLATION: Digital outputs isolated from input circuitry
(lO^^n, 40pF typ).
ENVIRONMENT:
OUTPUT CONNECTOR:
INSTALLATION:
Model 1793 Operate: 0 to 55°C, 0 to 80% RH.
Storage: -25 to +70°C.
Model 6423 Operate: 20 to 30°C, 0 to 70% RH.
Storage: -25 to +55°C.
24-pin IEEE-488 standard connector.
Field installable, mounts within and powered from
meter. Adds 0.6kg (1.3 lbs), 10 watts.
Model 1793 Precludes 1788, 1792 installation.
Model 6423 Precludes 6422, 6428 installation.
ACCESSORIES AVAILABLE: 1.8m (6 ft.) IEEE Cable Keithley Model 7008.
1-2

MODEL 1793/6423
INITIAL PREPARATION
SECTION 2. INITIAL PREPARATION.
2-1. INTRODUCTION.
2-2. This section provides information for incoming
inspection, preparation for use, and installation of
the Model 1793/6423.
2-3. UNPACKING AND INSPECTION.
2-4. The Model 1793/6423 was carefully inspected,
both mechanically and electrically before shipment.
Upon receiving your IEEE output option, unpack all
items from the shipping container and check for any
obvious damage which may have occured during
transit. Report any damages to the shipping agent.
Retain and use the original packaging materials if
reshipment is required. The following items
(Keithley Part No. in parentheses) are shipped with
all orders of your option:
a. Model 1793
1) PC-524 Assembly (30370D)
2) Shield Assembly (30I07C)
3) Replacement Top Cover (30409C)
4) A copy of this Instruction Manual
5) Separate Optional Cable (Model 7008), as
ordered.
b. Model 6423
1) PC-524 Assembly (30494D)
2) Shield Assembly (30133B)
3) Back Panel Assembly (30496A)
4) A copy of this Instruction Manual
5) Separate Optional Cable (Model 7008), as
ordered.
2-5. MODEL 1793 INSTALLATION.
2-6. The Model 1793 is installed internally in the
Model 177, 179, I79-20A or 480 and is powered by its
own line operated power supply. Installation of the
Model 1793 precludes use of the Model 1788 Battery
Pack and 1792 BCD Output. Refer to Figure 2-1 and
install the Model 1793 as follows:
\
WARNING
Disconnect the line cord before removing
the case cover.
a. Turn off power and disconnect line cord.
b. Turn the DMM bottom side up and loosen the
four screws in the bottom cover.
c. Hold the top and bottom covers together to
prevent their separation and turn the DMM over to
the normal position.
d. Lift off the top cover and the calibration
shield if installed. Remove the Model 1788 Battery
Pack or Model 1792 BCD Option if installed. The
four plastic spacers must remain in place on the
upright studs projecting through the main printed
circuit board.
NOTE
Do not discard the calibration shield.
This shield must be installed during
calibration, as described in the
Instruction Manual for your instrument.
e. If the Model 1788 was removed, set the LINE/
BAT switch on the main printed circuit board to the
LINE position.
f. Set the Line Voltage Switch (S50I) on the 1793
to the proper voltage (IIOV or 230V).
g. The 1793 is powered by the AC line. Discon
nect J1003 from its mating receptacle on the instru
ment's mother board (J1005 on the Model 480), and
reconnect to P1003A on the 1793. Connect J1003B of
the 1793 to P1003 on the instrument's mother board
(PI005 on the Model 480).
2-1

INITIAL PREPARATION
MODEL 1793/6423
h. Connect P1008 to its mating recepticle on the
printed circuit board (J1002 on the Model 480 and
J1008 on the Models 177, 179, a 179-20A).
j. Install the Model 1793 in the instrument so
that it rests on the plastic spacers. The ground
clip must make contact with the upper side of the
shield on the Model 1793.
k. Set up the DIP switch, S502, for the proper
mode of operation and timing/address as explained in
the Operating Instructions (paragraph 3-3).
1. Install the top cover that was shipped with
the Model 1793. This cover has a hole to accom
modate the connector of the Model 1793.
m. Save all removed parts for reinstallation in
the event that the 1793 is to be removed at a later
date.
2-7. MODEL 6423 INSTALLATION.
2-8. The Model 6423 is installed internally in the
Model 642 Electrometer mainframe and is powered by
its own line operated power supply. Installation of
the Model 6423 precludes use of the Model 6422 BCD
Output and the Model 6428 Battery Adapter. Refer to
Figure 2-2 and install the Model 6423 as follows:
X
WARNING
Disconnect the line cord before removing
the case cover.
a. Turn off power and disconnect the line cord.
b. Remove the four attaching screws and remove
the top cover.
c. Remove and replace the back panel plate with
the plate that is furnished with the Model 6423.
(Remove the Model 6422 or 6428 if installed.)
d. Remove the front four attaching screws from
the mother board and replace them with the metal
spacers, as shown in Figure 2-2. These spacers may
fit snugly and require use of a wrench to install
them. Take care not to cross thread or tighten them
too tight.
e. Connect P10G8 to J1013 on the mother board.
After making the connection, place the printed cir
cuit board outside of the Model 642 so that there is
no strain on the cable and the board will be out of
the way during installation of the shield and
spacers in the following steps.
f. Place the shield on the spacers and attach
with the four screws, as shown. The printed circuit
board will not fit properly unless the shield is in
stalled with the nut plates on the bottom side and
with the hole pattern positioned as illustrated.
g. Install the four spacers into the shield.
h. Place the printed circuit board on the spacers
(component side down) and attach it with four
screws.
i. Attach the output connector (J501) to the back
panel plate using two No. 6 hex head bolts and two
No. 6 kep nuts (see Component Layout 30494D - page
6- ).
j. Disconnect the AC power line at the mother
board of the 642 (J/P 1006) and reconnect to P1003A
of the 6423. Connect J1003B of the 6423 to P1006 of
the 642.
k. Set the Line Voltage Switch (S501) on the
6423 to the proper line voltage (llOV or 230V).
1. Set up the DIP switch, S502, for the proper
mode of operation and timing/address as explained in
the Operating Instructions (paragraph 3-3).
m. Reinstall the case top cover.
n. Save all removed parts for reinstallation in
the event that the 6423 is to be removed at a later
date.
2-9. MODEL 1793/6423 OUTPUT CONNECTOR.
2-10. The Model 1793/6423 uses a 24-pin connector
(J501) which will interface with IEEE-488 1978 con
nector.
2-11. An optional cable accessory is available for
interfacing the 1793/6423 with external equipment.
The Model 7008 is a 1.8m (6 ft.) IEEE Cable.
2-2

MODEL 1793/6423
INITIAL PREPARATION
P1003A
PLASTIC SPACER
(4 PLACES)
LINE VOLTAGE SWITCH
(S501)
P1008
I GROUND CLIP
J1008
DMM CASE
FIGURE 2-1. Installation of Model 1793
2-3

INITIAL PREPARATION
MODEL 1793/6423
MODIFIED PC-524
(30494D)
_i
STANDOFF (8) f
SHIELD
PIOOB/
J1013
a
642
MAINFRAME
FIGURE 2-2. Installation of Model 6423.
2-4

MODEL 1793/6423
OPERATION
SECTION 3. OPERATION
3-1. INTRODUCTION.
3-2. This section provides information needed for
proper operation of the Model 1793/6423.
3-3. OPERATING INSTRUCTIONS.
3-4. TALK ONLY mode - When switch 6 of S502 (see
Figure 3-1) is closed, the interface is in the TALK
ONLY mode of operation. In this mode the positions
of switches 1, 2 and 3 determine the output rate as
defined in Table 3-1. The positions of switches 4
and 5 do not affect operation.
3-5. ADDRESSABLE mode - When switch 6 is in the
open position the interface is in the ADDRESSABLE
mode. Switches 2 through 5 now determine the
address of the interface. These switches correspond
to the addresses 2^ through 2^ respectively.
The even address corresponding to switches 2 through
5 is the NON-TRIGGER ADDRESS. The next odd address
is the TRIGGER ADDRESS, Examples of NON-TRIGGER and
TRIGGER ADDRESSES are shown in Table 3-2.
3-6. The ADDRESSABLE NON-TRIGGER mode sends the
most recent reading on the BUS immediately after
receiving its address. The A/D is always in the RUN
mode after receiving its NON-TRIGGER ADDRESS. If
the NON-TRIGGER ADDRESS is received while the A/D is
in the HOLD mode, a reading won't be outputted until
400msec. (1 conversion) later.
3-7. When the interface receives its TRIGGER
ADDRESS while the A/D is in the RUN mode, the pre
sent conversion is completed and 1 more complete
conversion occurs. The last reading is outputted on
the BUS and the A/D is now in the HOLD mode. Each
time the TRIGGER ADDRESS is now received, a single
A-D conversion will be triggered and 400msecs later
the data will be outputted to the BUS. Table 3-3
shows the time delays when going from one address
mode to another. If a NON-TRIGGER ADDRESS is
received within 400msec. of a previous NON-TRIGGER
ADDRESS, data will not be outputted until the new
conversion is complete.
TABLE 3-1
Switch positions for TALK ONLY MODE.
S7 S6 S5
S4
S3 S2 SI OUTPUT RATE
OUTPUT INTERVAL
X 1
XX
0
0 0
2.5 rdgs/sec 400 msec
X 1
X X
00
1 25 rdgs/minute
2.4 sec
X 1
X X
0
1
0
6
rdgs/minute lOsec
X 1
X X
0
1 1
1 rdg/minute
1 Min.
X 1
X X 1
0 0
12
rdgs/hour 5 Min.
X 1
X X 1
0
1
4
rdgs/hour
15 Min.
X 1 X X 1 1
0
1
rdg/hour 60 Min.
X=Don't
Care
l=Closed 0=Open
TABLE 3-2
Example of Non-Trigger and Trigger Addresses
Switch Setting
Non-Trigger Address
Trigger Address
(always even)
(always odd)
^ ^ S5
S4 ^
S2
SI
X 0 0 0
0
1 X
2
3
X 0 1
0 0 0
X
16
17
X 0 11
00
X
24
25
X 0 0 0
00
X
0
1
X=Don't Care
l=Closed 0=Open
3-1

OPERATION
MODEL 1793/6423
TABLE 3-3
Address To Address Time Delays
A/D MODE
CONDITION
BEFORE
OUTPUT
AFTER
OUTPUT DELAY UNTIL BUS OUTPUT
POWER ON
Run
NON-TRIGGER ADDRESS
RECEIVED
Run Run <lmsec
TRIGGER ADDRESS
RECEIVED
Run Hold 400-800msecs
TRIGGER ADDRESS
RECEIVED
Hold Hold 400msec
NON-TRIGGER ADDRESS
RECEIVED
Hold
Run 400msec
NON-TRIGGER ADDRESS
RECEIVED
Run Run
<lmsec if >400msec since last
address. 1 to 400msec if
<400msec since last address
3-8. Secondary Addressing. Due to settling time
of the A-D converter, it may be necessary to use the
Secondary Addressing mode of the 1793/6423 to
achieve triggered readings within the rated accuracy
of the instrument.
3-9. Secondary Addressing may also be used to
change the terminator from a CR-LF to LF-CR to be
compatible with all controllers (e.g. DEC 11V03).
Table 3-4 defines the Secondary Addresses.
Mode Select
Not Used
3-10. If no Secondary Address is sent, the default
condition is Secondary Address 0. The Secondary
Address must be present within 1msec after receiving
the primary address.
TABLE 3-4
Secondary Addresses
Secondary
Address
Triqqered Period
Terminator
0
400msec
CR-LF
1
400msec
LF-CR
2
1.2 sec
CR-LF
3
1.2 sec
LF-CR
FI6UK 3-1. SS02
3-2

MODEL 1793/6423
OPERATION
3-11. Using the 1793/6423 with the PET Computer.
The standard PET Computer comes with an IEEE 488
Port which can be used as a low cost controller. A
limitation of the PET, however, is that once a
device has been addressed to talk, it must respond
within 65msec. If a response is not received within
this time, the PET will proceed to the next BASIC
instruction. Table 3-5 is a suggested method to
circumvent this limitation of the PET.
3-12. To get a 400msec triggered reading with pro
gram in Table 3-5, change the address to 25. To get
a 1.2 sec. triggered reading, add the FOR NEXT loop
as shown in Table 3-6.
3-13. It is not recommended to use Secondary
Addressing with the 1793/6423 and the PET due to the
timing limitation.
TABLE 3-5
Program for the 1793/6423 and the PET.
TABLE 3-6
Program for a 1.2 Sec. Triggered Reading
BASIC INSTRUCTIONS
REMARKS
10 OPEN 1,24 I, is the logical file num
ber. 24 is the Primary
Address (can be from 4 to
29).
20 INPUT #1,0$
DATA is inputted to file I
from device with Primary
Address 24. D$ is the name
given to the incoming data.
30 IF ST=2 THEN 20
ST is the status bit; TIME
OUT Read error. The pro
gram remains in this loop
until data is received.
40 PRINT D$
The incoming data is
printed on the CRT.
BASIC INSTRUCTION
10 OPEN 1,25
15 FOR N = 1 to 3
20 INPUT# 1,D$
30 IF ST=2 THEN 20
35 NEXT N
40 PRINT D$
REMARKS
This loop gets 3 readings,
but only outputs the latest
reading.
End of loop.
*Remarks same as Table 3-5
3-3

MODEL 1793/6423
THEORY OF OPERATION
SECTION 4. THEORY OF OPERATION.
4-1. INTRODUCTION.
4-2. This section contains functional descriptions
of the Model 1793/6423 circuitry. The overall oper
ation of the 1793/6423 is depicted by the flow dia
gram in Figure 4-1.
4-3. The 1793/6423 is controlled by a 6802uP, a PIA
and 512 bytes of program memory. The uP contains an
internal oscillator and 128 bytes of RAM. An exter
nal 4MHz crystal is provided for the oscillator.
The PIA provides the I/O necessary to convert iso
lated serial data from the instrument to parallel
ASCII Data. It also performs the handshaking neces
sary to control the IEEE BUS. The program is stored
in 512 bytes of EPROM; the first 504 bytes are at
address 8000 to 81F8 Hex, the last 8 bytes are the
interrupt vectors addressed from FFF8 to FFFF Hex.
4-4. POWER SUPPLY.
4-5. The 1793/6423 has its own power supply derived
from AC line voltage, relay-controlled by the
instrument's 5-volt power supply. When the instru
ment is turned on, the relay activates the inter
face, an RC circuit (56Kn, 4.7uF) holds the micro
processor and PIA reset line below .8 volts for the
required 20msec after Vcc reaches 5 volts. Once the
reset line becomes approximately 4 volts, the micro
processor begins executing instructions.
4-6. PARALLEL TO SERIAL CONVERSION.
4-7. Parallel BCD data from the instrument is con
verted to serial data which is sent over one opto-
isolator to the processor. A strobe line provided
by the A/D pulses low for each of the 5 BCD digits
when an A/D conversion is complete (every 400
msecs).
4-8. The 4021 8 stage shift register inputs paral-
lej_ or serial data, depending on the state of the
P/S line. The 4018 divides the lOOKHz clock from
the instrument down to lOKHz to clock the shift reg
ister. When new BCD is not bein^ presented (the
strobe line remaining Low), the P/S line is low and
the data presented at the serial input is shifted
out Q8. The serial input is tied low so that Q8
always remains low when new BCD data is not
present.
4-9l. When new BCD is present (every 400 msecs), the
P/S line goes high as a result of the strobe pulsing
high. This causes the data present at PI - P8 to be
latched in the shift register and shifted out of Q8
at a 10 KHz rate.
4-10. The first bit shifted out is P8 which is
permanently tied low. The next bit P7 is tied high
and is used as a sync bit to signal the processor
that BCD data will immediately follow. Bits P6, P5,
P4 and P3 are the BCD code for a single digit,
beginning with the most significant digit. P2 and
PI contain the sign and overrange information.
4-11. Three inverters of U502 buffer Q8 to provide
the current sink necessary to drive the opto LED.
The data opto-isolator is used in the emitter fol
lower configuration to provide a uniform turn-on,
turn-off time (approx. 20 ysec). Since the data is
being sent asynchronously, the absolute turn-on,
turn-off times are not critical. A timing diagram
showing Parallel to Serial Conversions is given in
Figure 4-2.
4-12. SERIAL TO PARALLEL CONVERSION.
4-13. The processor looks at the serial data from
the opto and loops until the data goes high (the
sync bit P7). It then looks at the opto output at
100 usec. (1/lOKHz) intervals to sense the serial
data. After PI (the overrange bit) has been
received, the processor waits for another sync bit.
This process continues for 10 msecs until all five
digits of the latest reading are selected.
4-14. BUS OPERATION.
4-15. At turn-on of the instruments, or if an IFC
(interface clear) is executed, the processor reads
the DIP switches through the U513 tri-state buffers.
4-16. ADDRESS ACCEPTANCE.
4-17. The process of the 1793/6423 accepting its
address from the interface is as follows:
a. The controller sets DAV HIGH and ATM low which
clocks a 0 to the Q output of the D flip-flop. This
sets MDAC low and NRFD high indicating to the con
troller that the data has not yet been accepted.
The ATM going to low also programs the 3446 BUS
DRIVER for NDAC and NRFD to be sent on the BUS, and
DAV to be received from the BUS.
b. The uP then reads the address being sent
through the U504 BUS TRANSCEIVER on the PIA I/O BUS.
It then presets the flip-flop which sets NDAC high
and NRFD low to indicate that the data has been
accepted.
c. After all listeners on the BUS have accepted
the address, the DAV line will go low indicating
that the data on the BUS is no longer valid.
4-1

THEORY OF OPERATION
MODEL 1793/6423
( Power On ^
or IFC )
TALK
ONLY MODE
OUTPUT DATA TO
488 BUS
AM I
ADDRESSED
7
DELAY, SET BY
SWITCH SETTING
WAIT FOR NEW
READING FROM
INSTRUMENT
WHICH
ADDRESS
7
NON-TRIGGER
TRIGGER
WAS I
IN TRIGGER
MODE
7
GET A NEW
READING
ALREADY
IN TRIGGER
MODE
7
GET A NEW
READING
HAS THE
PRESENT RDG
BEEN OUTPUTED
YET
GET r NEW
REAPINGS
l.Rsec
TRIGGER
PERIOD
7
GET A NEW
READING
AOOns
GET A NEW
READING
INTERRUPT
HO n A-n
ACCEPT THE
ADDRESS EROIl
THE CONTROLLER
SECONDARY
ADDRESS
OUTPUT THE
I'EUEST READING
nu THE "88 PUS
UHICI
ADDRES
DRiriARY
ADDRES
FT FLAGS
DEPENDING ON
ADDRESS
SET FLAGS,
lUnp TO TEST
ADORE
Interrupts are generated by the
controller sending out an
address.
4-2
FIGURE 4-1. 1793/6423 Flow Diagrain

MODEL 1793/6423
THEORY OF OPERATION
4-18. DATA SENDING.
4-19. If the address received corresponds to the
switch settings, the interface will send the latest
reading on the BUS. The process of sending data on
the BUS is as follows;
a. Set PB4 high to put U504 in the send mode and
program NDAC and NRFD as inputs and DAV as an out
put.
b. Set the DAV line high to indicate it to all
listeners that data is not yet valid.
c. Present valid data on the U504 BUS Driver.
d. The NRFD line is sensed until it goes high
indicating that all listeners are ready for data.
e. DAV is made low to indicate that the data is
now valid.
f. The NDAC line is sensed until it goes high
indicating that all listeners have accepted the
data.
g. DAV is set high to indicate the data is no
longer valid.
Eight of these handshake procedures are necessary to
send 1 complete reading over the BUS (sign, 5
digits, carriage return, line feed). When the IFC
line is made low by a controller, a non-maskable
interrupt will be executed which will put the inter
face into a TALKER IDLE STATE.
ln.ec
VALID
P3. P4, P5. P6.(U501)
STROBE
P/S (U501).
PARALLEL BCD DATA
f LATCHED IN A02I
f
Siisec
SERIAL
DATA
Q8 (U501)
1^ ^
FIGURE 4-2, Timing Diagram
4-3

MODEL 1793/6423
MAINTENANCE
SECTION 5. MAINTENANCE.
5-1. INTRODUCTION.
5-2. This section contains test point data, a veri
fication procedure, and special handling procedures
for static sensitive devices of the 1793/6423.
5-3. TEST POINT DATA.
5-4. The Model 1793/6423 has 4 test points that can
be used for troubleshooting or confidence testing.
Test points are described in Table 5-1. Test points
are accessible by removing the instrument top cover
as described in the installation procedure. The
test points are labeled on the 1793/6423 PC-Board.
5-5. 1793/6423 VERIFICATION PROCEDURE.
5-6. After the 1793/6423 has been properly
installed, its operation can be verified for both
the ADDRESSABLE and TALK ONLY modes of operation.
5-7. ADDRESSABLE mode verification.
a. Disconnect the instrument's line cord and set
the 1793/6423 for the ADDRESSABLE mode. Address
selection is described in the Operating Instructions
(par. 3-5).
b. Connect the 1793/6423 to a controller and
apply power to the instrument.
c. Address the 1793/6423 to Talk with it's even
NON-TRIGGER ADDRESS. Confirm that the reading
received by the controller is the same as the
instrument's displayed reading (less decimal point).
d. Address the 1793/6423 with it's odd TRIGGER
ADDRESS. Note that the data is delayed before being
received by the controller (400 to 800 msec.).
Again, verify that the controller's reading agrees
with the instrument's reading.
5-8. TALK ONLY mode verification.
a. Set the 1793/6423 in the TALK ONLY mode
select a desired output rate as explained in
Operator's Instructions (par. 3-4).
and
the
b. Connect the 1793/6423 to a listener, such as a
printer, and verify that the output rate corresponds
to the switch settings. Also, verify that the data
agrees with the instrument's reading.
TABLE 5-1
Test Point Data
Test
Point
Signal
Reference
+ 5V
+5V Supply ±250mV
1793/6423 COM
TPI STROBE - pulsed high 5
times (1 for each digit)
every 400 msec. The 5
pulses are 2 msec, apart.
Refer to timing diagram
for STROBE (Figure 4-2).
Instrument
Input Low
TP2
ISOLATED SERIAL DATA -
Approximately 9 msec, of
positive going pulses
occuring at 400 msec,
intervals. The number of
pulses is dependent on the
displayed reading. (See
Figure 5-1)
1793/6423 COM
TP3
The system clock (02) is a
IMHz, 0 to 4V square wave.
1793/6423 COM
Test Conditions: Instruments and 1793/6423 Turned
On.
No Controller attached.
■ynsec-
.39Unsec.
FIGURE 5-1. Isolated Serial Data
5-1

MAINTENANCE
MODEL 1793/6423
5-9. SPECIAL HANDLING OF STATIC SENSITIVE DEVICES.
5-10. CMOS and MOS devices are designed to function
at very high impedance levels for low power consump
tion. For this reason, a normal static charge build
up on your person or clothing can be sufficient to
destroy these devices. The following steps list the
static sensitive devices in your Model 1793/6423 and
provide instructions on how to avoid damaging them
when they must be removed/replaced.
a. Static sensitive devices;
Keith ley
Reference
Part No.
Designation
IC-I30
U501
IC-106
U502
IC-I45
U503
IC-153
U507
LSI-8
U509
LSI-I8
U511
b. The above integrated circuits should be
handled and transported only in protective con-
tainers. Typically they will be received in metal
tubes or static protective foam. Keep the devices
in their original containers until ready for use.
c. Remove the devices from their protective con
tainers only at a properly grounded work bench or
table, and only after grounding yourself by using a
wrist strap.
d. Handle the devices only by the body,
touch the pins.
NOTE
Do not
P1008 is shipped with a piece of con
ductive foam covering the pins to prevent
static damage. This conductive foam
should be replaced if you disconnect P1008
to remove the 1793/6423 from its host
i nstrument.
e. Any printed circuit board into which a device
is to be inserted must also be grounded to the bench
or table.
f. Use only anti-static type solder suckers.
g. Use only grounded tip soldering irons.
h. After soldering the device into the board, or
properly inserting it into the mating receptacle,
the device is adequately protected and normal
handling can be resumed.
5-2

HODEL 1793/6423
REPLACEABLE PARTS
SECTION 6. REPLACEABLE PARTS.
6-1. GENERAL.
6-2. This section contains information for ordering
replacement parts. The Replaceable Parts List
(Table 6-1) is arranged in alphabetical order of the
Circuit Designations of the components. A Cross-
Reference List of Manufacturers, containing their
address, is given in Table 6-2.
6-3. ORDERING INFORMATION.
6-4. To place an order, or to obtain information
concerning replacement parts, contact your Keithley
representative or the Factory. See the inside front
cover for addresses. When ordering, include the
following information.
a. Equipment Model Number.
b. Part Description.
c. Circuit Designation (if applicable).
d. Keithley Part Number.
6-5. SCHEMATIC.
6-6. Model 1793/6423; Schematic No. 30386D, Page
6-7. COMPONENT LAYOUTS.
6-8. Physical locations of parts are shown in the
following component layouts.
TABLE 6-1
Replaceable Parts List
Ci rcuit
Schematic
PO-Board Location
Mfr. Mfr.
Keithley
Desig.
Description
Location 1793
6423 Oode Desig.
Part No.
AT501 10, Optically-Ooupled
Isol ator
0-6 E-3 F-3
F-I FOD 820
10-82
AT502 10, Optically-Ooupled
Isolator
0-5
E-3 F-3
F-I FOD 820
10-82
C501
Oap, 4.7mF, 35V, EAL
A-4 D-2
E-2 ITT
TAPA 75
4.7yFK20
0-179-4.7
C502 Oap, 4700yF, 16V, Ea
0-3
D-3
E-3 OAI
0SD4700-
16-1
0-290-4700
C503
Oap, O.lpF, 16V, OerD
G-3
0-4
D-4 OLB
UK16-104 0-238-.1
C504 Oap, O.lyF, 16V, OerD
E-3
D-4 E-4 OLB
UK16-104 0-238-.1
C505
Oap, O.lyF, 16V, OerD
D-4 D-4
E-4 OLB
UK16-104 0-238-.1
0506
Oap, O.lyF, 16V, OerD
F-1
D-4
E-4 OLB
UK16-104
0-238-.1
0507
Oap, 22pF, 500V, OerD
0-5
B-5
D-5 OLB
DD220 0-22-22p
0508
Oap, 22pF, 500V, OerD
D-5
0-5 D-5 OLB
OD220
0-22-22P
0509
Oap, 4.7wF, 35V, IK.
E-5
D-5
E-5 ITT
TAPA 75
4.7yFK20
0-179-4.7
0510
Oap, 0.02yF, 500V, OerD
B-3
B-3
0-3 ERI
811-00025
U0203H
0-22-.02
0R501
Bridge Rectifier, Silicon
B-3
D-3
E-3
G-I
W04-M RF-46
0R502
Diode, Silicon, 75mA, 75V
B-4
0-3
D-3 T-I
IN914
RF-28
0R503
Diode, Silicon, 75nA, 75V
H-4
0-3
D-3 T-I
IN914 RF-28
0R504 Diode, Silicon, 75mA, 75V
H-5
0-3
B-3 T-I
IN914
RF-28
0R5O5
Diode, Silicon, 75mA, 75V
E-5
D-5
E-5 T-I
IN914
RF-28
F501
Fuse, Slo-Blo, 1/8A, 250V,
SAG
B-2
B-3
0-3 BUS
MDL
FU-20
6-1

REPLACEABLE PARTS
MODEL 1793/6423
TABLE 6-1
Replaceable Parts List (Cont'd)
Circuit Schematic PC-Board
Location Mfr. Mfr.
Keithley
Desig. Description Location
1793 6423 Code
Desig.
Part No.
J501
1793 Connector, IEEE
H-3 A-3
—
AMP 552791-1
CS-377
J501 6423 Connector, IEEE
H-3
~
B-3 TRW
222-22-24-100 OS-324
J1003B Connector Msg, Female,
3 pin (Contacts CS-276)
B-1 B-2
C-5 MOL 2139-3
CS-287-3
K501 Relay, 5V, Reed Type
B-4
C-3 D-3 COT UF-40097
RL-56
P1003A Connector, Male, 3 Pin
A-1
B-3 C-3
MOL 09-75-
1031
CS-379-3
PI 008 1793 Cable Assembly
A-4
D-1
—
K-I
— 27961A-1
P1008 6423 Cable Assembly
A-4
~
E-1 K-I
—
27961A-2
R501 150ft, 5%, 1/4W, CarbF
C-5
D-3 E-2
MEP CR-25*
R-76-150
R502 lOKft, 5%, 1/4W, CarbF
C-6
E-3 F-2 MEP CR-25*
R-76-10K
R503
100Kfi,5%, 1/4W, CarbF
C-6
E-3 F-3
MEP
CR-25*
R-76-100K
R504 2,4Kfi, 5%, 1/4W, CarbF
H-4
C-3
D-3 MEP CR-25*
R-76-2.4K
R505 2.4Kfi, 5%, 1/4W, CarbF
H-5 C-3 D-3
MEP
CR-25*
R-76-2.4K
R506 6.2Kft, 5%, 1/4W, CarbF
H-4
C-3 D-3
MEP CR-25*
R-76-6.2K
R507 6.2Kft, sr., 1/4W, CarbF
H-6
C-3
D-3 MEP
CR-25*
R-76-6.2K
R508 lOOKfi, sr, 1/4W, CarbF
C-6 D-3
E-3 MEP
CR-25*
R-76-100K
R509
150Kft, 5%, 1/4W, CarbF
D-6
D-3 E-3
MEP CR-25*
R-76-150
R510 lOKft, Sr, 1/4W, CarbF
C-6 D-3
E-3
MEP CR-25*
R-76-10K
R511 lOKft, 5%, 1/4W, CarbF
D-6 D-3
E-3 MEP
CR-25*
R-76-10K
R512
(A-I)
lOKft, 5%. Thick Film
Several E-5 F-5
K-I
— TF-99
R513 56Kft, 5%, 1/4W, CarbF
E-5
D-5
E-5 MEP
CR-25*
R-76-56K
6-2