Stanford Research Systems SIM984 Operation And Service Manual

Operation and Service Manual

Isolation Amplifier

SIM984

Distribution in the UK & Ireland

Characterisation,
Measurement &
Analysis

Stanford Research Systems

Lambda Photometrics Limited

Lambda House Batford Mill
Harpenden Herts AL5 5BZ
United Kingdom

E: [e-mail]
W: www.lambdaphoto.co.uk
T: [phone]
F: [phone]

Revision 1.13 • March 11, 2013

Certification

Stanford Research Systems certifies that this product met its published specifications at the time
of shipment.

Warranty

This Stanford Research Systems product is warranted against defects in materials and workman­ship for a period of one (1) year from the date of shipment.

Service

For warranty service or repair, this product must be returned to a Stanford Research Systems
authorized service facility. Contact Stanford Research Systems or an authorized representative
before returning this product for repair.

Information in this document is subject to change without notice.

Copyrightc Stanford Research Systems, Inc., 2013. All rights reserved.

Stanford Research Systems, Inc.
1290–D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: [phone] • Fax: [phone]

www.thinkSRS.com • e-mail: [e-mail]

Printed in U.S.A. Document number 9-01691-903

SIM984 Isolation Amplifier

Contents

General Information iii

Symbols ............................. iv

Notation ............................. v

Specifications .......................... vi

1 Getting Started 1 – 1

1.1 Introduction to the Instrument ............. 1–2

1.2 Front-Panel Operation .................. 1–2

1.3 SIM Interface ........................ 1–4

2 Remote Operation 2 – 1

2.1 Index of Common Commands .............. 2–2

2.2 Alphabetic List of Commands .............. 2–3

2.3 Introduction ........................ 2–4

2.4 Commands ......................... 2–4

2.5 Status Model ........................ 2–13

3 Circuitry 3 – 1

3.1 Circuit Descriptions .................... 3–2

3.2 Schematic Diagrams ................... 3–3

i

ii Contents

SIM984 Isolation Amplifier

General Information

Service

The SIM984 Isolation Amplifier, part of Stanford Research Systems’
Small Instrumentation Modules family, is a wide bandwidth, low
noise isolation amplifier for use with analog signals from DC to
1 MHz.

Do not install substitute parts or perform any unauthorized modifi­cations to this instrument.

The SIM984 is a single-wide module designed to be used inside the
SIM900 Mainframe. Do not turn on the power until the module is
completely inserted into the mainframe and locked in place.

iii

iv General Information

Symbols you may Find on SRS Products

Symbol Description

Alternating current

Caution - risk of electric shock

Frame or chassis terminal

Caution - refer to accompanying documents

Earth (ground) terminal

Battery

Fuse

On (supply)

Off (supply)

SIM984 Isolation Amplifier

General Information v

Notation

The following notation will be used throughout this manual.

WARNING

CAUTION

A warning means that injury or death is possible if the instructions
are not obeyed.

A caution means that damage to the instrument or other equipment
is possible.

Typesetting conventions used in this manual are:

• Front-panel buttons are set as [Button].

• Front-panel indicators are set as Overload.

• Remote command names are set as *IDN?

• Literal text other than command names is set as OFF.

Remote command examples will all be set in monospaced font. In
these examples, data sent by the host computer to the SIM984 are set
as straight teletype font, while responses received by the host
computer from the SIM984 are set as slanted teletype font.

SIM984 Isolation Amplifier

vi General Information

Specifications

Performance Characteristics

Isolation voltage ±1000 V (max)

Leakage current

Isolation capacitance 1000 pF

Isolation Mode Rejection Ratio (IMRR)

Maximum input

Input impedance

Input noise (typ.)

Input offset drift

Output voltage range ±10 V

Output current

Output resistance

Output offset

Output offset drift

Output noise (typ.)

Gain × 1, × 10, × 100

Gain accuracy

THD

Frequency range

Output Slew rate

Operating temperature 0◦Cto40◦C, non-condensing

Power

<2 μA at 1000 Vdc

150 dB at DC
±10 V
1MΩ
15 nV/√Hz @ 1 kHz
3 μV/◦C (typ.)

±20 mA (max.)
50 Ω
±0.1 V, adjustable
1mV/◦C (typ.)
80 μVrms (100Hz bandwidth)
200 μVrms (10kHz bandwidth)

1.5 mVrms (1MHz bandwidth)

±0.5%

0.005% (1 kHz, 600 Ω load)
DC to 100 Hz (low BW)
DC to 10 kHz (medium BW)
DC to 1 MHZ (high BW)
25 V/μs (Vout = 20Vpp)

+5 V (100 mA)
±15 V (300 mA)
+24 V (100 mA)

General Characteristics

Interface

Connectors banana jack (2 front)

Weight 1.5 lbs

Dimensions 1.5W ×3.6H ×7.0D

Serial (RS-232) through SIM interface

BNC (1 front, 1 rear)
DB–15 (male) SIM interface

SIM984 Isolation Amplifier

1 Getting Star ted

In This Chapter

This chapter gives you the necessary information to get started
quickly with the SIM984 Isolation Amplifier.

1.1 Introduction to the Instrument ............. 1–2

1.1.1 Overview ..................... 1–2

1.1.2 Power-on State .................. 1–2

1.2 Front-Panel Operation .................. 1–2

1.2.1 Inputs ....................... 1–2

1.2.2 Gain ........................ 1–2

1.2.3 Bandwidth ..................... 1–3

1.2.4 Output ....................... 1–3

1.3 SIM Interface ....................... 1–4

1.3.1 SIM interface connector ............. 1–4

1.3.2 Direct interfacing ................. 1–5

1–1

1–2 Getting Started

1.1 Introduction to the Instrument

The SIM984 Isolation Amplifier is a low-noise, programmable gain
amplifier for isolating analog signals from DC to 1 MHz.

1.1.1 Overview

The basic function of the SIM984 is to isolate and (possibly) amplify
an analog signal. The input presents a 1 MΩimpedance between the
red and black banana jacks, but is high impedance (floating) between
each input jack and chassis ground. A maximum of ±1000Vdc can be
between either jack and ground, but the potential between the input
jacks must be less than ±10 V. The input is DC coupled.

A gain of ×1, ×10, or ×100 can be set from the front panel. The output
bandwidth is also adjustable from the front panel, with three choices
of high-frequency cut-off: 100 Hz, 10 kHz, and 1 MHz. Finally, the
output DC offset can be trimmed using a thin screwdriver accessing
the “Offset” hole near the output BNC.

1.1.2 Power-on State

The SIM984 stores its operation state (gain and bandwidth configu­ration) in non-volatile memory. At power-on, the SIM984 will return
to its previous configuration after a brief system check and initializa­tion.

1.2 Front-Panel Operation

The front panel of the SIM984 (see Figure 1.1) provides a simple
operator interface.

1.2.1 Inputs

The input to the SIM984 is through the red and black banana jacks in
the front-panel “INPUT” block.

WARNING

1.2.2 Gain

The banana jacks are isolated from the chassis for use with insulated
test leads. If the user connects a BNC–to–Banana adaptor to the
SIM984 to allow inputs from a BNC-terminated cable, it is critical
that no dangerous voltages be applied to the cable, as the exposed
shield of the input BNC could create an electrical hazard.

User gain settings of ×1, ×10, and ×100, are selected with the left and
right [Gain] buttons.

SIM984 Isolation Amplifier

1.2 Front-Panel Operation 1–3

1.2.3 Bandwidth

1.2.4 Output

SIM984 Isolation Amplifier

Figure 1.1: The SIM984 front and rear panels.

User bandwidth settings of DC–100 Hz, DC–10 kHz, and DC–1 MHz
are with the left and right [Bandwidth] buttons.

The amplified, band-limitedsignal appears at the(ground-referenced)
BNC connectors on the front and rear panels. Each output connec­tion is through a 50Ω resistor. For normal operation, the user should
not need to terminate the output. If a 50 Ω termination is applied,
the output signal will be divided in half.

If the output signal exceeds ±10 V, the output overload detection is
activated. This is indicated by the red OVLD near the top of the
“OUTPUT” block on the front panel.

The SIM984 output offset voltage may be trimmed by adjusting the

1–4 Getting Started

output offset through the front-panel access hole in the “OUTPUT”
block.

1.3 SIM Interface

The primary connection to the SIM984 Isolation Amplifier is the rear­panel DB–15 SIM interface connector. Typically, the SIM984 is mated
to a SIM900 Mainframe via this connection, either through one of the
internal Mainframe slots, or the remote cable interface.

It is also possible to operate the SIM984 directly, without using the
SIM900 Mainframe. This section provides details on the interface.

CAUTION

The SIM984 has no internal protection against reverse polarity, missing
supply, or overvoltage on the power supply pins. Misapplication of power
may cause circuit damage. SRS recommends using the SIM984 together
with the SIM900 Mainframe for most applications.

1.3.1 SIM interface connector

The DB–15 SIM interface connector carries all the power and commu­nications lines to the instrument. The connector signals are specified
in Table 1.1

Pin Signal Src ⇒ Dest Description

1 SIGNAL GND MF ⇒ SIM Ground reference for signal
2

−STATUS SIM ⇒ MF Status/service request (GND = asserted, +5V= idle)

3

RTS MF ⇒ SIM HW handshake (not used in SIM984)

4

CTS SIM ⇒ MF HW handshake (not used in SIM984)

5

−REF 10MHZ MF ⇒ SIM 10 MHz reference (no connection in SIM984)

6

−5V MF ⇒ SIM Power supply (no connection in SIM984)

7

−15 V MF ⇒ SIM Power supply

8

PS RTN MF ⇒ SIM Power supply return

9

CHASSIS GND Chassis ground

10

TXD MF ⇒ SIM Async data (start bit = “0”=+5 V; “1” = GND)

11

RXD SIM ⇒ MF Async data (start bit = “0”=+5 V; “1” = GND)

12

+REF 10MHz MF ⇒ SIM 10 MHz reference (no connection in SIM984)

13

+5V MF ⇒ SIM Power supply

14

+15 V MF ⇒ SIM Power supply

15

+24 V MF ⇒ SIM Power supply

Direction

Table 1.1: SIM Interface Connector Pin Assignments, DB-15

SIM984 Isolation Amplifier

1.3 SIM Interface 1–5

1.3.2 Direct interfacing

The SIM984 is intended for operation in the SIM900 Mainframe, but
users may wish to directly interface the module to their own systems
without the use of additional hardware.

The mating connector needed is a standard DB–15 receptacle, such
as Amp part # 747909-2 (or equivalent). Clean, well-regulated sup­ply voltages of ±15,+5 and +24 VDC must be provided, following
the pin-out specified in Table 1.1. Ground must be provided on
pins 1 and 8, with chassis ground on pin 9. The −STATUS signal
may be monitored on pin 2 for a low-going TTL-compatible output
indicating a status message.

1.3.2.1 Direct interface cabling

If the user intends to directly wire the SIM984 independent of the
SIM900 Mainframe, communication is usually possible by directly
connecting the appropriate interface lines from the SIM984 DB–15

1

plug to the RS-232 serial port of a personal computer.

Connect RXD

from the SIM984 directly to RD on the PC, TXD directly to TD. In
other words, a null-modem style cable is not needed.

1.3.2.2 Serial settings

To interface directly to the DB–9 male (DTE) RS-232 port typically
found on personal computers, a cable must be made with a female
DB–15 socket to mate with the SIM984, and a female DB–9 socket
to mate with the PC’s serial port. Separate leads from the DB–15
need to go to the power supply, making what is sometimes know as
a “hydra” cable. The pin-connections are given in Table 1.2.

The initial serial port settings at power-on are: 9600 Baud, 8–bits,
no parity, 1 stop bit, and no flow control. The serial baud rate and
word size are fixed, but the parity may be changed with the PARI
command.

1

Although the serial interface lines on the DB-15 do not satisfy the minimum
voltage levels of the RS-232 standard, they are typically compatible with desktop
personal computers

SIM984 Isolation Amplifier

1–6 Getting Started

DB–15/F to SIM984 Name

DB–9/F
10 ←→ 3 TxD
11 ←→ 2 RxD

5 Computer Ground

to P/S

7 ←→ −15 VDC
13 ←→ +5VDC
14 ←→ +15VDC
15 ←→ +24VDC

8,9 ←→ Ground (P/S return current)

1 ←→ Signal Ground (separate wire to Ground)

Table 1.2: SIM984 Direct Interface Cable Pin Assignments

SIM984 Isolation Amplifier

2 Remote Operation

In This Chapter

This chapter describes operating the SIM984 over the serial interface.

2.1 Index of Common Commands ............. 2–2

2.2 Alphabetic List of Commands ............. 2–3

2.3 Introduction ........................ 2–4

2.3.1 Power-on configuration ............. 2–4

2.3.2 Buffers ....................... 2–4

2.3.3 Device Clear .................... 2–4

2.4 Commands ........................ 2–4

2.4.1 Command Syntax ................. 2–5

2.4.2 Notation ...................... 2–6

2.4.3 Examples ..................... 2–6

2.4.4 Amplifier Commands .............. 2–7

2.4.5 Status Commands ................ 2–7

2.4.6 Interface Commands ............... 2–9

2.5 Status Model ....................... 2–13

2.5.1 Status Byte (SB) .................. 2–13

2.5.2 Service Request Enable (SRE) .......... 2–14

2.5.3 Standard Event Status (ESR) .......... 2–15

2.5.4 Standard Event Status Enable (ESE) ...... 2–15

2.5.5 Communication Error Status (CESR) ...... 2–15

2.5.6 Communication Error Status Enable (CESE) . 2 – 16

2–1

2–2 Remote Operation

2.1 Index of Common Commands

symbol definition

i,j Integers
z

Literal token

(?)

var
{var }

[var ]

Required for queries; illegal for set commands
parameter always required
required parameter for set commands; illegal for queries
optional parameter for both set and query forms

Amplifier

GAIN(?) {i} 2 – 7 Gain
BWTH(?) {i} 2 – 7 Bandwidth

Status

*STB? [i] 2 – 7 Status Byte
*SRE(?) [i,] {j} 2 – 7 Service Request Enable
*CLS 2 – 7 Clear Status
*ESR? [i] 2 – 8 Standard Event Status
*ESE(?) [i,] {j} 2 – 8 Standard Event Status Enable
CESR? [i] 2 – 8 Comm Error Status
CESE(?) [i,]{j} 2 – 8 Comm Error Status Enable
OVLD? 2 – 8 Overload Condition
PSTA(?) {z} 2 – 9 Pulse −STATUS Mode

Interface

*RST 2 – 9 Reset
*IDN? 2 – 9 Identify
*OPC(?) 2 – 9 Operation Complete
CONS(?) {z} 2 – 10 Console Mode
LEXE? 2 – 10 Execution Error
LCME? 2 – 11 Command Error
PARI(?) {z} 2 – 11 Parity
TOKN(?) {z} 2 – 11 Token Mode
TERM(?) {z} 2 – 12 Response Termination

SIM984 Isolation Amplifier

2.2 Alphabetic List of Commands 2–3

2.2 Alphabetic List of Commands



*CLS 2 – 7 Clear Status
*ESE(?) [i,] {j} 2 – 8 Standard Event Status Enable
*ESR? [i] 2 – 8 Standard Event Status
*IDN? 2 – 9 Identify
*OPC(?) 2 – 9 Operation Complete
*RST 2 – 9 Reset
*SRE(?) [i,] {j} 2 – 7 Service Request Enable
*STB? [i] 2 – 7 Status Byte

B

BWTH(?) {i} 2 – 7 Bandwidth

C

CESE(?) [i,]{j} 2 – 8 Comm Error Status Enable
CESR? [i] 2 – 8 Comm Error Status
CONS(?) {z} 2 – 10 Console Mode

G

GAIN(?) {i} 2 – 7 Gain

L

LCME? 2 – 11 Command Error
LEXE? 2 – 10 Execution Error

O

OVLD? 2 – 8 Overload Condition

P

PARI(?) {z} 2 – 11 Parity
PSTA(?) {z} 2 – 9 Pulse −STATUS Mode

T

TERM(?) {z} 2 – 12 Response Termination
TOKN(?) {z} 2 – 11 Token Mode

SIM984 Isolation Amplifier

2–4 Remote Operation

2.3 Introduction

Remote operation of the SIM984 is through a simple command lan­guage documented in this chapter. Both set and query forms of
most commands are supported, allowing the user complete control
of the isolation amplifier from a remote computer, either through the
SIM900 Mainframe or directly via RS-232 (see Section 1.3.2.1).

2.3.1 Power-on configuration

The settings for the remote interface are 9600 baud with no parity
and no flow control, and local echo disabled (CONS OFF).

Most of the SIM984 instrument settings are stored in non-volatile
memory, and at power-on the instrument returns to the state it was
last in when power was removed. Exceptions are noted in the com­mand descriptions.

Reset values of parameters are shown in boldface.

2.3.2 Buffers

2.3.3 Device Clear

2.4 Commands

Incoming data from the host interface is stored in a 32-byte input
buffer. Characters accumulate in the input buffer until a command
terminator (either CR or LF) is received, at which point the mes­sage is parsed and executed. Query responses from the SIM984 are
buffered in a 32-byte output queue.

If the input buffer overflows, then all data in both the input buffer
and the output queue are discarded, and an error is recorded in the
CESR and ESR status registers.

The SIM984 host interface can be asynchronously reset to its power­on configuration by sending an RS-232-style break signal. From
the SIM900 Mainframe, this is accomplished with the SIM900 SRST
command; if directly interfacing via RS-232, then use a serial break
signal. After receiving the Device Clear, the interface is reset and
CONS mode is turned OFF. Note that this only resets the communi-
cation interface; the basic function of the SIM984 is left unchanged;
to reset the instrument, see *RST.

This section provides syntax and operational descriptions for reo­mote commands.

SIM984 Isolation Amplifier

2.4 Commands 2–5

2.4.1 Command Syntax

The four letter mnemonic (shown in CAPS) in each command se­quence specifies the command. The rest of the sequence consists of
parameters.

Commands may take either set or query form, depending on whether
the “?” character follows the mnemonic. Set only commands are
listed without the “?”, query only commands show the “?” after the
mnemonic, and optionally query commands are marked with a “(?)”.

Parameters shown in {}and [ ] are not always required. Parameters in
{}are required to set a value, and are omitted for queries. Parameters
in [ ] are optional in both set and query commands. Parameters listed
without any surrounding characters are always required.

Do not send()or{}or [ ] as part of the command.

Multiple parameters are separated by commas. Multiple commands
may be sent on one command line by separating them with semi­colons (;) so long as the input buffer does not overflow. Commands
are terminated by either CR or LF characters. Null commands
and whitespace are ignored. Execution of command(s) does not
begin until the command terminator is received.

tokens

Token parameters (generically shown as z in the command de­scriptions) can be specified either as a keyword or integer value.
Command descriptions list the valid keyword options, with each
keyword followed by its corresponding integer value. For example,
to set the response termination sequence to CR+LF, the following
two commands are equivalent:

TERM CRLF —or— TERM 3

For queries that return token values, the return format (keyword or
integer) is specified with the TOKN command.

SIM984 Isolation Amplifier

2–6 Remote Operation

2.4.2 Notation

The following table summarizes the notation used in the command
descriptions:

symbol definition

i,j Integers
z

Literal token

2.4.3 Examples

(?)
var
{var }

[var ]

Required for queries; illegal for set commands
parameter always required
required parameter for set commands; illegal for queries
optional parameter for both set and query forms

Each command is provided with a simple example illustrating its
usage. In these examples, all data sent by the host computer to
the SIM984 are set as straight teletype font, while responses
received the host computer from the SIM984 are set as slanted
teletype font.

The usage examples vary with respect to set/query, optional param­eters, and token formats. These examples are not exhaustive, but are
intended to provide a convenient starting point for user program­ming.

SIM984 Isolation Amplifier

2.4 Commands 2–7

2.4.4 Amplifier Commands

GainGAIN(?) {i}

Set (query) input gain {to state i=(0 (×1), 1 (×10), 2 (×100))}.

GAIN 2

BandwidthBWTH(?) {i}

Set (query) the signal bandwidth {to state i=(0 (DC–100 Hz), 1 (DC–
10 kHz), 2 (DC–1 MHz))}.

BWTH?Example:

1

2.4.5 Status Commands

The Status commands query and configure registers associated with
status reporting of the SIM984.

Status Byte*STB? [i]

Reads the Status Byte register [bit i].

Execution of the *STB? query (without the optional bit i) always
causes the −STATUS signal to be deasserted. Note that *STB? i will

not clear −STATUS, even if bit i is the only bit presently causing the

−STATUS signal. See also the PSTA command.

The OVLD bit in *STB is cleared upon reading.

*STB?Example:

1

Service Request Enable*SRE(?) [i,] {j}

Set (query) the Service Request Enable register [bit i] {to j}.

*SRE 0,1Example:

Clear Status*CLS

*CLS immediately clears the ESR, CESR, and the OVLD bit in the

Status Byte.

*CLSExample:

SIM984 Isolation Amplifier

2–8 Remote Operation

Standard Event Status*ESR? [i]

Reads the Standard Event Status Register [bit i].

Upon executing *ESR?, the returned bit(s) of the ESR register are
cleared.

*ESR?Example:

64

Standard Event Status Enable*ESE(?) [i,] {j}

Set (query) the Standard Event Status Enable Register [bit i] {to j}.

*ESE 6,1Example:
ESE?

64

Comm Error StatusCESR? [i]

Query Comm Error Status Register [for bit i].

Upon executing a CESR? query, the returned bit(s) of the CESR
register are cleared.

CESR?Example:

0

Comm Error Status EnableCESE(?) [i,]{j}

Set (query) Comm Error Status Enable Register [for bit i] {to j}

CESE?Example:

0

Overload ConditionOVLD?

Query Overload Condition. If the SIM984 is overloading, OVLD?
returns 1; otherwise 0.

OVLD?Example:

0

SIM984 Isolation Amplifier

2.4 Commands 2–9

Pulse −STATUS ModePSTA(?) {z}

Set (query) the Pulse −STATUS Mode {to z=(OFF 0, ON 1)}.

When PSTA ON is set, any new service request will only pulse the

−STATUS signal low (for a minimum of 1 μs). The default behavior
is to latch −STATUS low until a *STB? query is received.

At power-on, PSTA is set to OFF.

PSTA?Example:

OFF

2.4.6 Interface Commands

Interface commands provide generic control over the interface be­tween the SIM984 and the host computer.

Reset*RST

Reset the SIM984 to default configuration.

After *RST, the gain is set to ×1 and the bandwidth to DC–100 Hz.
This is equivalent to the following command sequence:

GAIN 0; BWTH 0

*RSTExample:

Identify*IDN?

Read the device identification string.

The identification string is formatted as:

Stanford

where ****** is the 6-digit serial number, and #.# is the firmware
revision level.

*IDN?Example:

Stanford

Operation Complete*OPC(?)

Operation Complete. Sets the OPC flag in the ESR register.

The query form *OPC? writes a 1 in the output queue when complete,
but does not affect the ESR register.

*OPCExample:

Research Systems,SIM984,s/n******,ver#.#

Research Systems,SIM984,s/n003075,ver1.02

SIM984 Isolation Amplifier

2–10 Remote Operation

Console ModeCONS(?) {z}

Set (query) the Console mode {to z=(OFF 0, ON 1)}.

CONS causes each character received at the Input Buffer to be copied
to the Output Queue.

At power-on and Device-Clear, CONS is set to OFF.

CONS?Example:

0

Execution ErrorLEXE?

Query the last execution error code. A query of LEXE? always clears
the error code, so a subsequent LEXE? will return 0. Valid codes are:

Value

*STB? 12; LEXE?; LEXE?Example:

3
0

The error (3, “Invalid bit,”) is because *STB? only allows bit-specific
queries of 0–7. The second read of LEXE? returns 0.

Definition

0 No execution error since last LEXE?

Illegal value

1

Wrong token

2

Invalid bit

3

Command not ready

16

SIM984 Isolation Amplifier

2.4 Commands 2–11

Command ErrorLCME?

Query the last command error code. A query of LCME? always clears
the error code, so a subsequent LCME? will return 0. Valid codes are:

Value

Definition

0 No execution error since last LCME?

Illegal command

1
2

Undefined command
Illegal query

3

Illegal set

4

Missing parameter(s)

5

Extra parameter(s)

6

Null parameter(s)

7
8

Parameter buffer overflow
Bad floating-point

9

Bad integer

10

Bad integer token

11

Bad token value

12

Bad hex block

13

Unknown token

14

*IDNExample:
LCME?

4

The error (4, “Illegal set”) is due to the missing “?”.

SIM984 Isolation Amplifier

ParityPARI(?) {z}

Set (query) parity {to z = (NONE 0, ODD 1, EVEN 2, MARK 3, SPACE 4)}.

After power-on, modules default to PARI NONE.

PARI EVENExample:

Token ModeTOKN(?) {z}

Set (query) the Token Query mode {to z=(OFF 0, ON 1)}.

If TOKN ON is set, then queries to the SIM module that return to­kens will return the text keyword; otherwise they return the decimal
integer value.

Thus, the only possible responses to the TOKN? query are ON and 0.

On reset, TOKN is set to OFF.

TOKN OFFExample:

2–12 Remote Operation

Response TerminationTERM(?) {z}

Set (query) the term sequence {to z=(NONE 0, CR 1, LF 2, CRLF 3,
LFCR 4)}. The term sequence is appended to all query responses
sent by the module, and is constructed of ASCII character(s) 13 (car­riage return) and 10 (line feed). The token mnemonic gives the
sequence of characters.

At power-on, TERM is set to CRLF.

TERM?Example:

3

SIM984 Isolation Amplifier

2.5 Status Model 2–13

2.5 Status Model

The SIM984 status registers follow the hierarchical IEEE–488.2 for­mat. A block diagram of the status register array is given in Figure 2.1.

There are two categories of registers in the SIM984 status model:

Event Registers : These read-only registers record the occurrence of defined

events. When the event occurs, the corresponding bit is set
to 1. Upon querying an event register, any set bits within it
are cleared. These are sometimes known as “sticky bits,” since
once set, a bit can only be cleared by reading its value. Event
register names end with SR.

Enable Registers : These read/write registers define a bitwise mask for their cor-

responding event register. If any bit position is set in an event
register while the same bit position is also set in the enable
register, then the corresponding summary bit message is set.
Enable register names end with SE.

2.5.1 Status Byte (SB)

The Status Byte is the top-level summary of the SIM984 status model.
When masked by the Service Request Enable register, a bit set in the
Status Byte causes the −STATUS signal to be asserted on the rear­panel SIM interface connector.

Typically, −STATUS remains asserted (low) until a *STB? query is
received, at which time −STATUS is deasserted (raised)

1

. After clear-

ing the −STATUS signal, it will only be re-asserted in response to a

1

but see the PSTA command

Communication Error Status

7

7

6

5

4

3

2

1

0

CESR CESE

6

5

4

3

2

1

0

Status Byte

CESB

7

7

6

5

4

3

2

1

0

SB SRE

X

5

4

3

2

1

0

MSS

ESB

IDLE

undef

undef

undef

OVLD

-

STATUS

Standard Event Status

PON: Power On

URQ: User Request

CME: Command Error

EXE: Execution Error

DDE: Device Error

QYE: Query Error

INP: Input Buffer Error

OPC: Operation Complete

7

6

5

4

3

2

1

0

ESR ESE

OVR: Input Buffer Overrun

HWOVRN: Hardware Overrun
7

6

5

4

3

2

1

0

FRAME: Framing Error

DCAS: Device Clear

CTSH: CTS Halted

RTSH: RTS Halted

NOISE: Noise Error

PARITY: Parity Error

SIM984 Isolation Amplifier

Figure 2.1: Status Register Model for the SIM984.

2–14 Remote Operation

new status-generating condition.

Weight Bit Flag

1 0 OVLD
2

1 undef (0)

4

2 undef (0)

8

3 undef (0)

16

4 IDLE

32

5 ESB

64

6 MSS

128

7 CESB

OVLD : Overload Bit. Indicates whether an amplifier overload has

occurred.

IDLE : Indicates that the Input Buffer is empty and the command

parser is idle. Can be used to help synchronize SIM984 query
responses.

ESB : Event Status Bit. Indicates whether one or more of the enabled

events in the Standard Event Status Register is true.

MSS : Master Summary Status. Indicates whether one or more of

the enabled status messages in the Status Byte register is true.
Note that while −STATUS is released by the *STB? query, MSS
is only cleared when the underlying enabled bit message(s) are
cleared.

CESB : Communication Error Summary Bit. Indicates whether one or

more of the enabled flags in the Communication Error Status
Register has become true.

Most bits in the Status Byte are not cleared by the *STB? query. These
bits are only cleared by reading the underlying event registers, or by
clearing the corresponding enable registers. The one exception is the
OVLD bit, which itself is an event bit, and so is cleared by the *STB?
query.

2.5.2 Service Request Enable (SRE)

Each bit in the SRE corresponds one-to-one with a bit in the SB
register, and acts as a bitwise AND of the SB flags to generate the
MSS bit in the SB and the −STATUS signal. Bit 6 of the SRE is
undefined—setting it has no effect, and reading it always returns 0.
This register is set and queried with the *SRE(?) command.

This register is cleared at power-on.

SIM984 Isolation Amplifier

2.5 Status Model 2–15

2.5.3 Standard Event Status (ESR)

The Standard Event Status register consists of 8 event flags. These
event flags are all “sticky bits” that are set by the corresponding event,
and cleared only by reading or with the *CLS command. Reading a
single bit (with the *ESR? i query) clears only bit i.

Weight Bit Flag

1 0 OPC
2

1 INP

4

2 QYE

8

3 DDE

16

4 EXE

32

5 CME

64

6 URQ

128

7 PON

OPC : Operation Complete. Set by the *OPC command.

INP : Input Buffer Error. Indicates data has been discarded from the

Input Buffer.

QYE : Query Error. Indicates data in the Output Queue has been lost.

DDE : Device Dependent Error. This bit is undefined in the SIM984.

EXE : Execution Error. Indicates an error in a command that was

successfully parsed. Out-of-range parameters are an example.
The error code can be queried with LEXE?.

CME : Command Error. Indicates a parser-detected error. The error

code can be queried with LCME?.

URQ : User Request. Indicates a front-panel button was pressed.

PON : Power On. Indicates that an off-to-on transition has occurred

2.5.4 Standard Event Status Enable (ESE)

The ESE acts as a bitwise AND with the ESR register to produce the
single bit ESB message in the Status Byte Register (SB). It can be set
and queried with the *ESE(?) command.

This register is cleared at power-on.

2.5.5 Communication Error Status (CESR)

The Communication Error Status register consists of 8 event flags;
each of which is set by the corresponding event, and cleared only by
reading or with the *CLS command. Reading a single bit (with the
CESR? i query) clears only bit i.

SIM984 Isolation Amplifier

2–16 Remote Operation

Weight Bit Flag

1 0 PARITY
2

1 FRAME

4

2 NOISE

8

3 HWOVRN

16

4 OVR

32

5 RTSH

64

6 CTSH

128

7 DCAS

PARITY : Parity Error. Set by serial parity mismatch on incoming data

byte.

FRAME : Framing Error. Set when an incoming serial data byte is missing

the STOP bit.

NOISE : Noise Error. Set when an incoming serial data byte does not

present a steady logic level during each asynchronous bit­period window.

HWOVRN : Hardware Overrun. Set when an incoming serial data byte is

lost due to internal processor latency. Causes the Input Buffer
to be flushed, and resets the command parser.

OVR : Input Buffer Overrun. Set when the Input Buffer is overrun

by incoming data. Causes the Input Buffer to be flushed, and
resets the command parser.

RTSH : Undefined for the SIM984.

CTSH : Undefined for the SIM984.

DCAS : Device Clear. Indicates the SIM984 received the Device Clear

signal (an RS-232 break). Clears the Input Buffer and Output
Queue, and resets the command parser.

2.5.6 Communication Error Status Enable (CESE)

The CESE acts as a bitwise AND with the CESR register to produce
the single bit CESB message in the Status Byte Register (SB). It can
be set and queried with the CESE(?) command.

This register is cleared at power-on.

SIM984 Isolation Amplifier

3 Circuits

In This Chapter

This chapter presents a brief description of the SIM984 circuit design.

3.1 Circuit Descriptions ................... 3–2

3.1.1 Isolated power .................. 3–2

3.1.2 Input amplifier .................. 3–2

3.1.3 Output circuitry .................. 3–2

3.1.4 Digital control ................... 3–2

3.2 Schematic Diagrams ................... 3–3

3–1

3–2 Circuitry

3.1 Circuit Descriptions

3.1.1 Isolated power

Page 3 of the schematics shows the isolated supply that powers the
input stage. A spread-spectrum oscillator (U302) provides the AC
drive signal for power amplifier U301 to drive the isolating trans­former T301. The large capacitor C305 prevents any runaway DC
current from saturating the transformer, which could be generated
by offset voltages at U301.

3.1.2 Input amplifier

The upper portion of Page 2 shows the floating input amplifier. Gain
is controlled through latching relays U214 and U215, the control coils
of which are earth-referenced.

The (amplified) signal is optically coupled through U205, U206, U207,
and U208.

3.1.3 Output circuitry

3.1.4 Digital control

The (earth-referenced) output circuitry includes the output band­width control. This circuitry is on the lower portion of Page 2 of
the schematics. The overall AC gain is trimmed using VR202 at the
factory, and should not require user adjustment.

DC offset can be adjusted with VR203, accessed from the front panel
of the instrument. Note that the offset trim is referenced to the output,
and comes after the gain is applied.

The SIM984 is controlled by microcontroller U107.

A critical aspect of the design is the clock-stop circuitry implemented
by U102 and U105. A simple RC-oscillator is enabled or disabled at
pin 1 of U102, which is driven by synchronizing flip-flop U105B to
ensure that no “runt” clock pulses are produced that would violate
U107’s minimum clock periods. Four separate clock-starting signals
are combined by U106:

• Power-on reset

• Amplifier overload

• Incoming serial data

• Front-panel button press

SIM984 Isolation Amplifier

3.2 Schematic Diagrams 3–3

The fast start-time of the RC-oscillator ensures that incoming se­rial data will be correctly decoded by the microcontroller’s UART,
even when the clock is started by the serial start bit of the incoming
data. When the microcontroller has completed all pending activity,
it drives the STOP signal high (pin 71 of U107), effectively halting its
own processor clock. In this way, the SIM984 guarantees no digital
clock artifacts can be generated during quiescent operation.

3.2 Schematic Diagrams

Schematic diagrams follow this page.

Distribution in the UK & Ireland

Lambda Photometrics Limited

Lambda House Batford Mill
Harpenden Herts AL5 5BZ

Characterisation,
Measurement &
Analysis

United Kingdom

E: [e-mail]
W: www.lambdaphoto.co.uk
T: [phone]
F: [phone]

SIM984 Isolation Amplifier