Guralp Systems Limited
Section Index: 6.1 Using the command interpreter 6.2 General configuration 6.3 GPS and timing systems 6.4 Calibration

Chapter 6. Advanced usage

You can connect to the internal software of the CMG-EDU over its output serial port and communicate with it.

To enter command mode from Scream!, right-click on the digitizer's icon and select Terminal… from the menu that pops up. A window will open, and once the digitizer and computer are communicating properly you will see the prompt


If you prefer, you can use a terminal program on your computer (such as minicom on Linux, or hypertrm on Microsoft Windows) to connect to the CMG-EDU.

Whilst you are in terminal mode, data transfer will be interrupted. Some commands, such as SET-TAPS, require a reboot to take effect.

If you have problems connecting to the console, you should check that the serial port's options and baud rate are set correctly in Scream! or your terminal program. As supplied, the CMG-EDU expects connections at 19200 baud, with 8 data bits, no parity bit and 1 stop bit. No flow control is used.

6.1 Using the command interpreter

The CMG-EDU uses a FORTH-like interpreter to implement its features. To issue a command in FORTH, you must supply the arguments before the command, for example:


In FORTH, anything you enter is termed a word. New words (case insensitive) are placed on a stack. Some words are known to the system, and may represent commands; if a command finds itself at the top of the stack (e.g. because it is the last thing you typed), they will execute, remove themselves from the stack, and then remove further items from the stack to use as arguments. Thus, in the command


the 3 has no immediate effect, so stays on the stack; SENSOR-TYPE takes itself and the previous item (here 3) off the stack, then performs its action on the 3 .

If a command completes with nothing remaining on the stack, the digitizer will show the prompt ok. Otherwise, the prompt will remind you that the digitizer is waiting for you to complete the command. Some commands, such as SAMPLES/SEC, clear the stack automatically after they execute.

Some commands are interactive, and will ask you to provide extra information after you execute them. In the following sections, interactive commands are shown as example sessions, where information you enter is given in medium and messages returning from the CMG-EDU are given in bold.

Some seldom-used commands are in the extended dictionary. To access these commands, you need to enable this dictionary with the command ok-1. The standard commands will still be available. To return to normal operation, issue the command [seal]. While the extended dictionary is active, be very careful to type commands exactly as they are shown here. Mistyping a command with the dictionary unprotected can damage the internal code of the digitizer.

To close the terminal session and return to sending data, type


6.2 General configuration

6.2.1  SET-ID

Syntax: SET-ID (interactive)

Sets the system identifier and serial number of the CD24E1 to values you supply.


System Identifier ? (e.g. ALPHA,) DM24ID, Serial # ? (e.g. 1234,00) 4507,00

The system identifier you supply may contain up to 6 alphanumeric (0–9,A–Z) characters, and must have a comma after it. 6-character strings later than ZIK0ZJ are not permitted. The CD24E1 will pad any remaining space on the right with zeroes. If you want to use a system identifier less than 6 characters long, you should insert zeroes on the left to make it up to 6 characters. (Because of this, you cannot have a system identifier that begins with a zero.)

The serial number you supply must contain exactly 4 alphanumeric (0–9,A–Z) characters, followed by ,00 as shown.

You will need to RE-BOOT after issuing this command for it to take effect.

6.2.2  .IDS

Syntax: .IDS

Displays the System ID and stream IDs which are used to stamp all outgoing data packets, in the form

system-id stream-id sensor-type ok

where system-id is the name of the instrument (as reported in Scream!'s instrument list) and stream-id is the string which begins every data stream.

This command is in the extended dictionary; to use it, first issue the command ok-1 and finish with [seal].

6.2.3  BAUD

Syntax: 0 baud-rate BAUD

Sets the baud rate for the serial port on the CD24E1, in bytes per second. The CD24E1 has a single port, numbered 0. For example,

0 19200 BAUD

This will reset a standard CD24E1 to its default configuration.

The allowable values for baud-rate are 4800, 7200, 9600, 14400, 19200, 38400, 57600 and 1152 (n.b.), representing 115200.

You will need to RE-BOOT after issuing this command for it to take effect.

6.2.4  GO

Syntax: GO

Exits the terminal session and begins sending data. In Scream!, closing the terminal window has the same effect as this command.

If you have made configuration changes, you may need to RE-BOOT the digitizer instead of using this command.

6.2.5  RE-BOOT

Syntax: RE-BOOT

Causes the CD24E1 to reset.


Confirm with 'y' ? y

Responding to the confirmation message with anything other than y will abort the reset.

This command automatically closes Scream!'s terminal window.

6.3 GPS and timing systems

6.3.1  XGPS

Syntax: on/off XGPS

Switches on or off the GPS system. To save power consumption under normal operation, the CD24E1 only powers on the GPS occasionally to update timing information. You can override this with the XGPS command, where on/off is 0 to switch off the relay, and 1 to switch it on. Once switched on, the system will check the GPS, update the fix, and switch off for the period set by the HR-CYCLE command (see below).

6.3.2  HR-CYCLE

Syntax: interval HR-CYCLE

Sets the interval between GPS fixes. The system will power on the GPS system every interval hours and synchronize its internal clock with GPS timing signals. Once the internal clock is sufficiently close to GPS time, the GPS system will be automatically powered down for another interval hours.

Setting interval to 0 will make the CD24E1 leave the GPS on continuously. This is recommended if your installation has access to mains power.

6.3.3  SET-RTC

Syntax: year month day hour minute second centisecond SET-RTC

Sets the system's real time clock. This time will be used from power-up until it is corrected by an attached GPS. If you are not using GPS but are synchronizing from some other time source, you will need to re-issue this command regularly to ensure the CD24E1 does not drift.

You will need to RE-BOOT after issuing this command for it to take effect.

6.3.4  TIME?

Syntax: TIME?

Displays the current time as held in the system's real time clock. If a GPS is attached, this will be synchronized to it. The output is given in the form

year month day hour minute second centisecond ok

6.3.5  .FIX

Syntax: .FIX

Displays the current GPS timing fix. The GPS must be attached and powered up for this command to be valid; if it is not, you will see an error message. You can power up the GPS manually with the command XGPS.

The CD24E1 will reply in the form

.fix year month day hour:minute:second =>> Auto fix-mode SV#'s satellites ( number-of-satellites ) ok

where fix-mode is the fix type (either 2-D or 3-D) and satellites is a list of the satellites currently visible. The CD24E1 will carry out clock trimming only if a 3-D fix is available, which requires at least 3 satellites to be visible.

6.3.6  .POSITION


Displays the current reported GPS position, in the form

.position Lat latitude Long longitude ok

where latitude and longitude are displayed in degrees, minutes and seconds.

This command is in the extended dictionary; to use it, first issue the command ok-1 and finish with [seal].

6.4 Calibration


Syntax: Z freq-or-period unit SINEWAVE

Instructs the CD24E1 to inject a sine-wave calibration signal, starting on the zero crossing.

Z denotes the Z channel of the digitizer. This is used for the CMG-EDU's single component (whether vertical or horizontal.)

freq-or-period and unit together determine the frequency of the calibration signal. If unit is HZ, then freq-or-period is taken as a frequency, in Hz; if SECOND, then it is interpreted as a period, in s. For example:


freq-or-period must be an integer; if you want to specify a period of, for example, 0.5 s, you should specify it as 2 HZ instead.

The calibration signal will be automatically disconnected after 2 minutes if you have not altered the setting using the MINUTE command, described below.

Whilst the calibration signal is being generated, it is output on the channel MB as well as being fed into the sensor. Calibration is done by comparing the data from the MB channel with the sensor's normal data stream.


Note that the MB channel is a 16-bit channel whilst the signal is digitized at 24 bit resolution. If using Scream! to measure signal strengths, you will have to multiply values from the MB channel by 256 before comparing them with the normal signals.



Instructs the CD24E1 to inject a square-wave (step function) calibration signal, consisting of a positive step on the start of the next clock minute, followed by a negative step some minutes later (by default, 2). The calibration is disconnected the same number of minutes after the negative edge.

Z denotes the Z channel of the digitizer. This is used for the CMG-EDU's single component (whether vertical or horizontal.)

You can alter the duration of each step using the MINUTE command, described below.

6.4.3  MINUTE

Syntax: duration MINUTE

Sets for how long the next SINEWAVE calibration signal will be injected, or the period of the next SQUAREWAVE calibration signal.

duration is the desired interval, in minutes. If you now issue a SINEWAVE command, the calibration will last duration minutes; if the next calibration command is SQUAREWAVE, a positive step of duration minutes will be generated, followed by a negative step of a further duration minutes.

If you do not issue MINUTE, calibration signals will default to 2 minutes. This is to avoid the sensor and digitizer inadvertently being left in calibration mode. Issuing, e.g., 5 MINUTE will cause the next calibration signal to last 5 minutes, but later calibration signals will revert to a duration of 2 minutes. You will need to issue a MINUTE command before each injection.

Because of the way FORTH works, you can insert MINUTE commands into SQUAREWAVE or SINEWAVE commands, for example:



6.4.4  MINUTES ?

Syntax: MINUTES ? (note the space before ?)

Displays the current setting of the MINUTES variable, i.e. how long the next calibration signal will last.


Syntax: percentage %AMPLITUDE

Sets the calibration amplitude to the given percentage of the full-scale signal.

6.4.6  AMPLITUDE ?

Syntax: AMPLITUDE ? (note the space before ?)

Displays the current setting of the AMPLITUDE variable, i.e. the amplitude of the next calibration signal, as a percentage of the full-scale signal.

6.4.7  RESP

Syntax: value RESP

Switches the CMG-EDU between response modes according to value:

0 : broadband mode (standard);

1 : 1 second response mode (for monitoring mass positions.)

6.4.8  MASSES?

Syntax: MASSES?

Displays the current, instantaneous position of the three sensor masses, in counts (range ±8 000 000):

masses? z-position n/s-position e/w-position ok