Polling operation
This application note describes the flexible polling mode of the MLM-1000 in systems with version 1.3 firmware.
This application note assumes reader familiarity with the MLM -1000 Mooring Line Modem system.
Flexible polling overview
The polling feature provides the capability for the system to broadcast a configurable command string to SSM connected instruments e(.g. RBR loggers or third party instruments), and then retrieve the results.
The flexible aspect arises from the fact that the command string can be configured as per the requirements of the deployment.
The polling itself can be invoked two possible ways.
via a command from a host computer to the HEM (PNOW – poll now)
via enabling the autonomous polling feature of the HEM where it will perform a polling cycle at regular predetermined intervals.
The key steps in a polling cycle include:
The command string is transmitted as a broadcast from the HEM and thus received simultaneously by all the targeted SSM connected instruments
The broadcast address is a group address. Hence all or a targeted selection of instruments will receive the command sequence as per the group address configurations within the system
After transmitting the command sequence, the HEM waits a (configurable) latency period. The latency period must be set to be greater than the time it takes the instrument to take a sample and output the information on its serial link
Once the command is processed by the SSM attached instrument, the SSM will buffer the result (up to 1792 bytes) as it is transmitted by the connected instrument. Data payloads greater than 1792 bytes will result in the loss of the data for the bytes beyond 1792.
After waiting for the latency period, the HEM will access each targeted SSM in turn and retrieve the results of the instrument executing the polling command string.
Once all the results are retrieved, they will be transmitted via the serial port on the HEM to the serial data connected host link (e.g. RF modem)
Polling related modem configuration parameters
The following are excerpts from the OEM Command Reference, V2.
PNOW - Poll now
Command: PNOW
Response: see below
Purpose:Poll all SSMs now
Applies to: HEM
See also:EEPROM PDEL, PINT, PCMD, PADD, PSLPEN, PWUPEN, PWUPCHAR, PEN, PDISP
This command will trigger all RBR loggers or third party instruments connected to SSMs to respond to the poll command as specifed by the ee parameter PCMD. If applicable, data generated from a sample or otherwise sent to the SSMs will be reported back to the HEM (the sampling and reporting is referred to together as polling). The SSM serial port output will optionally transmit a serial wakeup character (if enabled) (e.g. <cr> for the RBR logger) followed by the command string as specified by the ee parameter PCMD. After a duration of PDEL, the HEM will collect the data from all the SSMs. Subsequently, the HEM will output all the data to its serial port at once.
This command performs the same function as a scheduled poll, however all but the logger output data will be muted on a scheduled poll. If non-RBR loggers/instruments are connected on the serial ports, this will produce unknown serial port output.
If already in an open channel, the response will be:
<t>*error* poll not allowed now<cr><lf>
If the poll fails at some point, the response will be:
<t>*error* poll<cr><lf>
After a successful poll, the response will be:
<t>poll complete OK<cr><lf>
Example: PNOW<cr>
<t>poll requested<cr><lf>
<ALL CONNECTED SSM LOGGER OUTPUT>
<t>poll complete OK<cr><lf>
PEN - Poll Enable
Parameter:
Description:
Values: 0, 1
Default: 0
Applies to:
See also:Command PNOW; EEPROM PINT, PCMD, PADD, PSLPEN, PWUPEN, PWUPCHAR, PDEL,PDISP
This parameter defines whether the scheduled polling should be enabled. Once enabled, this will trigger all instruments connected to (selected) SSMs to receive the command string specified by the PCMD ee parameter. For example, PCMD has been set to “F00” and this command sent to an RBR logger, causes the logger to immediately take a sample and report that sample back to the HEM, which will then output the data to its serial port.
Example: EE PEN 1<cr>
<t>poll enable PEN: 1<cr><lf>
PINT – Poll Interval Time
Parameter: Description: Values: 1-65535 Default: 5 Applies to:
PINT poll interval time (min)
PEN poll enable
HEM
HEM
See also:Command PNOW; EEPROM PEN, PCMD, PADD, PSLPEN, PWUPEN, PWUPCHAR, PDEL,PDISP
This parameter defines the polling interval of time in minutes. Example (2 hour polling interval): EE PINT 120<cr>
<t>poll interval time (min) PINT: 120<cr><lf>
Example(20minutepollinginterval): EE PINT 20<cr>
<t>poll interval time (min) PINT: 20<cr><lf>
PDEL - Poll Delay
Parameter:
Description:
Values: 50-3000
Default: 500
Applies to:
PDEL poll delay time (10ms)
HEM
See also:Command PNOW; EEPROM PINT, PCMD, PADD, PSLPEN, PWUPEN, PWUPCHAR, PEN,PDISP
This parameter defines the delay between the broadcast of command string as specified by the PCMD ee parameter to (selected) SSM connected instruments and the start of the retrieval of the instrument replies (should be longer than the time it takes the slowest instrument to respond).
Example: EE PDEL 1000<cr>
<t>poll delay time (10ms) PDEL: 1000<cr><lf>
PDISP - Poll Display
Parameter:
Description:
Values: 0, 1
Default: 0
Applies to:
See also:Command PNOW; EEPROM PINT, PCMD, PADD, PSLPEN, PWUPEN, PWUPCHAR, PDEL,PEN
This parameter enables the display of ‘<zero padded 6 digit ID>: ’ before all output received from an RBR logger or SSM connected third party instrument during a poll. If no output is received, the ID will be terminated with a ‘<cr><lf>’.
Poll output example:
123456: TIM 100623103500 22.9962 FET<cr><lf> 123457: <cr><lf>
036459: TIM 100623103500 24.2343 FET<cr><lf>
Example: EE PDISP 1<cr>
<t>poll display enable PDISP: 1<cr><lf>
PDISP poll display enable
PCMD – Poll Command String
Parameter: PCMD
Description: poll command string
Values: x00-xFF
Default: 46 30 30 (F00)
Applies to: HEM
Seealso:Command PNOW; EEPROM PEN, PINT, PDISP, PWUPEN, PSLPEN, PADD, PDEL,PWUPCHAR
This parameter defines the command string of up to 16 ASCII characters that the HEM transmits when it performs the polling function.
The command string is entered as a string of ASCII numbers that represent the command string. The command to display the command string slightly differs from the command to set the command string
Example of setting a poll command string of F00:
EE PCMD S 46 30 30<cr>
<t>poll command string PCMD: x46, x30, x30<cr><lf>
Example of displaying the poll command string:
EE PCMD <cr>
<t>poll command string PCMD: x46, x30, x30<cr><lf>
PWUPEN – Poll Wakeup Character Enable
Parameter:
Description:
Values: 0, 1
Default: 1
Applies to:
Seealso:Command PNOW; EEPROM PEN, PINT, PDISP, PCMD, PSLPEN, PADD, PDEL,PWUPCHAR
This parameter enables the transmission of a “throw away” serial character used to wake up an SSM connected instrument before the actual command used during the poll is transmitted to the instrument.
Example: EE PWUPEN 0<cr>
<t>poll wakeup char enable PWUPEN: 0<cr><lf>
PWUPEN poll wakeup character enable
PWUPCHAR – Poll Wakeup Character
Parameter: Description: Values: x00-xFF Default: x0D Applies to:
PWUPCHAR poll wakeup character
HEM
See also:Command PNOW; EEPROM PEN, PINT, PDISP, PWUPEN, PSLPEN, PADD, PDEL, PCMD
This parameter specifies the character transmitted on the serial link to the SSM connected instrument to wake it up. This is transmitted before the command specified by the ee parameter PCMD is sent.
Example: EE PWUPCHAR <cr>
<t>poll wakeup char PWUPCHAR: x0D<cr><lf>
Example: EE PWUPCHAR 0a<cr>
<t>poll wakeup char PWUPCHAR: x0A<cr><lf>
PSLPEN – Poll Sleep Enable
Parameter:
Description:
Values: 0,1
Default: 1
Applies to:
See also:Command PNOW; EEPROM PEN, PINT, PDISP, PWUPEN, PWUPCHAR, PADD, PDEL,PCMD
This parameter enables the transmission of the sleep command (ZZZ) to an SSM after the HEM has retrieved the results of the poll.
Example: EE PSLPEN 1<cr>
<t>poll sleep enable (zzz) PSLPEN: 1<cr><lf>
PSLPEN poll sleep enable
PADD – Poll Address
Parameter:
Description:
Values: 00-32
Default: 00
Applies to:
See also:Command PNOW; EEPROM PEN, PINT, PDISP, PWUPEN, PWUPCHAR, PSLPEN, PDEL,PCMD, GIDx
This parameter specifies the group identification number that will be addressed for the polling cycle.
Example: EE PADD 01<cr>
<t>poll address PADD: 01<cr><lf>
PADD poll address