SRS Labs SR530 Appendix B Introduction to the RS232, Baud Rate, Case 1 The Simplest Configuration

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Appendix B:

Introduction to the RS232

The 'RS232' is a standard for bit serial asynchronous data communication. The standard defines the format for data transmission, the electrical specifications for the signal levels, and the mechanical dimensions of connectors.

Despite the definition of a standard, there are so many permutations of control lines, data formats, and transmission speeds, that getting two RS232 devices to communicate usually requires some work.

In this section, we will provide some basic information to aid you in connecting your RS232 device to the SR530 Computer Interface.

CASE 1 - The Simplest Configuration.

In this case, one wire is used to send data from device A to device B and another wire is used to send data from device B to device A. Notice that pin 2 is an output on device A and an input on device B. (It is good practice to run the ground, pin 7, between the devices as well). The RS232 defines two types of devices; DTE (Data Terminal Equipment) and DCE (Data Communications Equipment.) An RS232 port on a computer may be either a DTE or DCE but nearly every terminal with an RS232 port is a DTE. RS232 ports on a computer which are intended to connect to a modem, such as the COM1: port on the IBM PC, are DTE. The SR530 is configured as DCE, and so it may be directly connected to ASCII terminals and to the COM: ports on IBM PC's and compatibles.

As an example, consider connecting an RS232 ASCII computer terminal to the SR530 using a 2 wire link. The terminal is a DTE and the SR530 is a DCE. To operate correctly, the SR530 and the terminal must have the same settings for baud rate, parity, and number of stop bits. The control lines in the RS232 Standard, which are used to indicate that a device is ready to accept

data, must also be connected correctly at the terminal end. If the terminal responds to a control line, it will believe that the SR530 is not ready to accept data (because the line is not passed in this example) and will therefore not send any data.

CASE 2 - RS232 with Control Lines.

The data lines are the same as in Case 1. In addition to the data lines, there are two control lines used:

CTS - Pin 5

"Clear to send" is a signal asserted by the DCE to tell the DTE that the DCE is ready to receive data.

DTR - Pin 20

"Data Terminal Ready" is a signal asserted by the DTE to tell the DCE that the DTE is ready to receive data.

The SR530 responds to the control lines as follows:

1)If the lines are not connected, the SR530 assumes that you are ready to receive data.

2)Data will not be transmitted from the SR530 if the DTR line (pin 20) is low. This is useful in the case when your program is not yet ready to receive data. If data transmission is not suspended, then data may be overwritten in your computer's UART (as it is not being retrieved by the program and so will be lost.) When this happens, the 'over-run' flag will be set in your computer's UART and it may be recognized by the operating system, generating an error message such as "I/O Device Error" (See the "W" command in the SR530 Command List for another way to slow data transmission.)

Baud Rate

The RS232 baud rate of the SR530 is switch selectable from 300 to 19.2K baud (see configuration switch setting in the front of this manual.) 19.2K baud means that data is transmitted at 19,200 bits/second. With one start bit, 2 stop bits, 8 data bits, and no parity bits, each ASCII character requires 573 ∝ sec to be transmitted (11bits/19.2K

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Contents Model SR530 Page Table of Contents Appendix C Gpib NON-OPERATING OperatingPage SR530 Specification Summary Gpib DemodulatorFront Panel Summary Enbw Abridged Command List Status Byte Definition Configuration SwitchesSensitivity Signal InputsSignal Filters SR510 Guide to Operation Front PanelChannel 1 Display Dynamic ReserveStatus Display SelectOffset Channel OutputOutput Channel Rel ChannelChannel 2 Display Expand ChannelRcosø Output Auto Phase Trigger Level Rsinø OutputReference Input Time Constant Reference ModePhase Controls Reference DisplayLocal and Remote PowerDefaults SR530 Guide to Operation Rear Panel Page Front Panel Status LEDs Command SyntaxSR530 Guide to Programming Communicating with the SR530Try-Out with an Ascii Terminal RS232 Echo and No Echo OperationLOW Norm High SR530 Command ListN1,n2,n3,n4 Page Bit ErrorsStatus Byte Common Software Problems include ResetTrouble-Shooting Interface Problems Common Hardware Problems includeSR530 with the Gpib Interface SR530 with the RS232 InterfaceSR530 with Both Interfaces Serial Polls and Service RequestsGpib with RS232 Echo Mode Measurement Example Lock-in TechniqueShielding and Ground Loops Understanding the SpecificationsPage Page SR530 Block Diagram DC Amplifiers and System Gain Signal ChannelPhase Sensitive Detectors Reference ChannelCircuit Description Demodulator and Low Pass Amplifier Reference OscillatorMicroprocessor Control Analog Output and ControlExpand Front PanelGpib Interface Power SuppliesRS232 Interface Calibration and Repair Multiplier AdjustmentsAmplifier and Filter Adjustments Replacing the Front-End Transistors Notch FiltersNon-Essential Noise Sources Appendix a Noise Sources and CuresPage Page Case 2 RS232 with Control Lines Case 1 The Simplest ConfigurationAppendix B Introduction to the RS232 Baud RateFinal Tip Stop BitsParity Voltage LevelsBus Description Appendix C Introduction to the GpibProgram Example IBM PC, Basic, via RS232 Appendix D Program ExamplesProgram Example IBM PC, Microsoft Fortran v3.3, via RS232 Page #include stdio.h Program Example IBM PC, Microsoft C v3.0, via RS232Page Program Example 4 IBM PC,Microsoft Basic, via Gpib ′INCREMENT X6 Output by 2.5 MV Program Example HP85 via Gpib Documentation Dpdt Oscillator Board Parts ListPC1 SW1BT1 Main Board Parts ListBR1 BR2SR530 Component Parts List SR530 Component Parts List CX1 22U MINPIN D Gpib ShieldedMPSA18 CY1FU1 SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List SR530 Component Parts List SR513 Assy SPSTX84PDT SR530 Component Parts List Static RAM, I.C Z80A-CPU#4 Flat TIE AnchorTranscover MicaFront Panel Board Parts List RED LD3 LD1LD2 Quad Board Parts List SR530 Component Parts List PC1 SR530 Component Parts List Miscellaneous Parts List SR530 Component Parts List

SR530, Lock-In Amplifier specifications

The SRS Labs Lock-In Amplifier, model SR530, is a powerful tool designed for high-precision measurements in the realm of scientific research and industrial applications. This state-of-the-art instrument excels in extracting small signals from noisy environments, making it an invaluable asset for experiments in fields such as physics, engineering, and materials science.

One of the main features of the SR530 is its ability to perform synchronous detection, which is key to improving signal-to-noise ratios. By utilizing a reference signal, the device correlates the incoming signal with the reference to effectively filter out noise, allowing for the accurate measurement of weak signals that might otherwise be obscured. This process of phase-sensitive detection is fundamental to the operation of the Lock-In Amplifier.

The SR530 offers a wide frequency range, covering from 0.1 Hz to 100 kHz. This broad frequency response allows it to handle a diverse array of signals, making it suitable for various applications including optical detection, capacitance measurements, and in many cases, voltammetry. The device is also equipped with multiple inputs and outputs, facilitating the integration with other laboratory equipment and enabling complex experimental setups.

Precision is further enhanced with its adjustable time constant, which allows users to optimize the response time based on experimental needs. The user can choose time constants from 10 microseconds to 10 seconds, accommodating fast dynamic measurements as well as those requiring stability over longer durations.

Another remarkable characteristic of the SR530 is its digital processing capabilities. The device features a highly accurate digital voltage measurement system, minimizing drift and ensuring long-term stability. Additionally, the use of microprocessors enhances data handling and allows for features such as programmable settings, facilitating automated measurements.

Moreover, the SR530 includes a range of output options, including analog outputs, which can be used for direct signal processing, as well as digital interfaces for integration with computers. This ensures that users can not only capture high-fidelity data but also analyze and display it efficiently.

In conclusion, the SRS Labs SR530 Lock-In Amplifier stands out due to its sophisticated technology, versatile features, and robust performance. Its precision, flexibility, and ease of use make it an ideal choice for researchers and engineers looking to unlock the potential of weak signal measurement in complex environments.
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