RD Controls Hardware Release Note 21.0 <P> CAMAC C1015 Module <P> Group3 DTM Teslameter Trigger Module

RD Controls Hardware Release Note 21.0

CAMAC C1015 Module

Group3 DTM Teslameter Trigger Module

R. West

January 28, 1991


The C1015 CAMAC module connects to a Group3 Model DTM-100 Series Hall Effect Teslameter via an RS232 interface. There is an RS232 port on the front of the C1015 module and also one on the rear of the module. The teslameter is connected to the module's rear RS232 port. The C1015 module is able to transmit to the teslameter input it receives through its front RS232 port. The module is also able to output to its front RS232 port all text received from the teslameter.

A 16-bit digital signal is input to the module via its external status connection on the rear of the module. A 16-bit trigger value is input to the module via a CAMAC command. Each time a new trigger value is received, the trigger bit in the module's status register is cleared. Every millisecond, an interrupt routine compares the digital input signal with the trigger value. When the two are equal, an event flag is set to notify the base-level processing routine in the module. The trigger bit in the module's status register is also set at this time. This status register may be read via a CAMAC command to determine if the external value has been matched. After the trigger occurs, the base-level routine of the module writes the ASCII character V to the teslameter to trigger a field measurement.

360 milliseconds after the V command is sent, the module writes an ASCII character F to the teslameter to read the field measurement triggered by the V command. The teslameter returns the value in the form of an ASCII text string and the module converts it to a binary value. The data-ready bit is then set in the module's status register. After the binary value is read via a CAMAC command, the module clears the data-ready bit.

Text communication from the teslameter to the module may be written into a circular text output buffer where it may be accessed via the Fast Online Protocol (FOP) CAMAC commands. The FOP commands may also be used to write characters into a circular text input buffer. This input can then be written to the teslameter to change or read various control paramenters. Response from the teslameter to such inputs are then accessed via the FOP commands.

Operational Considerations

The sequence of steps which normally occur when obtaining a triggered reading from the teslameter are the following:

Note that the trigger value and the external value must match exactly for a trigger event to be declared. If the trigger value is less than the external value and the external value is increasing or if the trigger value is greater than the external value and the external value is decreasing, no trigger event will ever be declared. If the external value is changing faster than the module can read it, an exact comparison may be missed and no trigger event will be declared.

After a trigger event occurs, the external value is not compared with the trigger value until the teslameter has obtained the requested field measurement, i.e., for the 360 ms interval between sending the V command and sending the F command. It is possible to set a new trigger value during this time, but no comparison of this new value against the external value will be done. Hence, the possibility of missing a comparison exists.

Ziptrack Application

The Ziptrack application uses the C1015 module to trigger and then obtain field readings from a teslameter probe which is on a moving cart (see Figure 1). A 16-bit value available from the motor controller indicates the position of the cart. The application program executing on the PC specifies a value to the C1015 module at which to trigger a field mesuarement. When this specified value matches the 16-bit digital input from the motor controller, the C1015 module writes a V command to the teslameter to trigger the reading and then after 360 milliseconds an F command to read the field value from the teslameter. The PC program polls the status of the C1015 module to determine when the new data is present and then reads the new value.

The PC program specifies positions of the cart which are at least 500 ms apart. Therefore, the field measurement trigger always occurs at least 140 ms after the previous field reading request. If the PC program sees the value of the cart position stop changing before the C1015 status indicates a field measurement has been triggered, the program sets an error flag and displays an error message.

Module Configuration

The C1015 module is based on the CAMAC 1111 single board computer:

On the front panel of the module are the following buttons and indicators:

RS232 Interface Configuration

The C1015 module has an RS232 I/O connector port on the rear of the module and also on the front. Each port's baud rate may be set to a value from 300 to 19200. RS232 serial data transmitted from the teslameter must be formatted as follows:

I/O Connector

There are 8 switches on the I/O connector used to indicate the type of device connected to the C1015 module. Switches 1 through 4 indicate the type of the connected meter and switches 5 through 8 indicate the baud rate. For the C1015 module, all switches must be in the OFF position to indicate a 9600 baud teslameter is connected.

Group3 Model DTM-100 Series Hall Effect Teslameter

The DTM-100 may be configured by use of DIP switches to transmit each new reading on the serial line in a known format at a maximum rate of 2.34 Hz.

Switch Settings

To enable the C1015 module to process data from the teslameter, the switches on the processor board of the teslameter must be set appropriately. The 16-position switch used to specify the serial data bit rate must be set to the 9600 position. The DIP switches must be set in the following manner:

The RS232 jumpers on the processor board must be connected in the following manner:

Message Formats

Upon request, the teslameter transmits to the C1015 module a string of ASCII characters which is terminated by a carriage return, line feed pair and which has the following format:



Teslameter Initialization

In addition to the physical switch settings, the C1015 module must send the DTM teslameter certain configuration commands whenever the module is reset or powered on:

CAMAC Functions

When a CAMAC operation is performed, the Z8002 processor executes a vectored interrupt to a routine which reads the CMCSLV data lines and determines the function code. A jump is then executed to the appropriate routine to process the request.

Function Code Descriptions

Data Format

The C1015 module converts the ASCII text string from the connected device to a signed 32-bit integer representing the floating point data value times 10 to the 7th power.

Status Format

The low byte of the status register contains a code providing information about the data text string returned by the attached teslameter:

If the teslameter is correctly configured and is returning valid data, the low byte of the status register will contain a 1, indicating the reading is in units of Tesla. The upper byte of the status register contains information about the triggger and the field measurement:


Diagnostic commands may be directly input to the module by connecting a computer terminal to one of the RS232 ports. A HELP menu displays the commands which are available to assist in trouble shooting. The following commands can be executed at a terminal:

Status LEDs

All status LEDs are cleared whenever a carriage return is received.

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