USB Interface Protocol

The Re:load Pro features a USB interface with serial port emulation (CDC), which supports a straightforward text-based protocol for controlling and monitoring the Re:load Pro and the attached test device. The Re:load Pro’s serial interface operates at 115200 baud 8/n/1.

Both commands and responses are line-based. Responses from the Re:load Pro are terminated with “\r\n”, and commands to the Re:load Pro need only be terminated with “\n” (“\r” will be silently ignored).

All commands generate at least one response line from the Re:load Pro. Some commands may generate multiple responses, and some conditions, such as interval monitoring, overtemperature and undervoltage may trigger unsolicited response lines from the Re:load Pro. Programs implementing the protocol should expect that they may receive such responses at any time, and code accordingly.

Commands and arguments are case-sensitive.

Command quick reference

Command Arguments Response Period Function
bl   ‘ok’ Once Enter bootloader mode
set I ‘set I’ Once Set current to I (mA)
mode MODE ‘mode MODE’ Once Set operating mode
read   ‘read mV mA’ Once Returns readings from the unit. Output may include other measurements on later firmware
reset   ‘ok’ Once Clear over temperature and under voltage alarm and sets current to 0
monitor INTERVAL See ‘read’ INTERVAL ms Sets up automatic printing of the read command (INTERVAL==0 to disable)
uvlo voltage uvlo voltage Once Sets the UVLO threshold in mV
on   ‘ok’ Once Turns the load on
off   ‘ok’ Once Turns the load off
debug   debugging data Once Prints various debugging information as ‘info’ lines
version   version info   Returns the current firmware version in dotted decimal
cal command arg varies Once Calibration commands. See calibration
clear   ‘ok’ Once Clears the totals for mAh and mWh

Command reference


Enters bootloader/firmware upgrade mode. Emits an ‘ok’ response, then enters bootloader mode. Any further serial communication will be received by the bootloader.

set [I]

Sets the current setpoint to I, expressed in milliamps. Responds with a ‘set’ response with the new current setpoint. This may differ from the provided setpoint if the provided setpoint was less than 0 or greater than the maximum supported current.

If I is not provided, reports the current setpoint without altering it.

mode MODE

Sets operating mode. Currently only ‘cc’ for constant current mode is supported. Responds with a ‘mode’ response with the new operating mode.


Returns a ‘read’ response with the voltage and current across the Re:load Pro.


When the Re:load Pro has disabled itself due to overtemperature or undervoltage, the ‘reset’ command sets the current setpoint to 0 and returns to normal operation. Returns an ‘ok’ response.

monitor INTERVAL

Enables monitoring with an interval of INTERVAL milliseconds. Every x milliseconds, a ‘read’ response will be returned until ‘monitor 0’ is sent to cease monitoring. The first response will occur after INTERVAL milliseconds, rather than immediately.

uvlo voltage

Sets the undervoltage cut off voltage to voltage, in millivolts. Returns ‘uvlo voltage’, with voltage in mV.


Turns the load on, enables the load to start drawing power


Turns the load off, stops the load drawing power.


Outputs a series of debugging information lines as ‘info’ messages.

cal SUBCOMMAND [arg]

Calibration master command. Supports several subcommands:

cal o

Calibrates ADC offsets. Sets ADC offset to the currently observed voltage and current, and returns ‘ok’. Only run with no leads attached to the Re:Load Pro.


Calibrates the ADC’s voltage gain. VOLTAGE should be the voltage across the Re:load Pro. Responds with ‘ok’.


Calibrates the ADC’s current gain. CURRENT should be the current across the Re:load Pro. Responds with ‘ok’.


Performs automatic DAC opamp offset trim, offset, and gain calibration based on the calibrated output of the ADC. Responds with ‘ok’. CURRENT is the maximum test current level to use in calibration.

From v1.6: No longer performs opamp offset trim calibration; this is now done with ‘cal t’ or manually with ‘cal O’

cal O [OFFSET]

Without an argument, returns the current opamp offset trim value, between 0 and 63 with a ‘cal O’ response. With an argument, sets the opamp offset trim.


Performs automatic opamp offset trim calibration. Responds with ‘ok’. CURRENT is the maximum test current level to use in calibration.


From v1.6: Returns the current firmware version number in a ‘version’ response.


This clears the totals for the mAh and mWh counters. This is the same as the menu item ‘Reset Totals’. Returns an ‘ok’ response.

Response reference


Returns the current and voltage across the Re:load Pro, in millivolts.


Sent when an invalid command was sent. MESSAGE is a human-readable message describing the problem.

mode MODE

Returns the current operating mode. Currently this will always be ‘cc’.

set I

Returns the current setpoint.


Indicates your command was received and acted on successfully.


Provides a human-readable information message about the Re:load Pro. Currently only used in response to the ‘debug’ command.


Returns the opamp offset trim value for the Re:load Pro’s internal opamp in response to a ‘cal O’ command.


Sent unsolicited when the FET in the Re:load Pro goes into overtemperature shutdown. Issue a ‘reset’ command to set the current setpoint to 0 and resume normal operation.


Sent unsolicited when the Re:load Pro detects an undervoltage condition. Issue a ‘reset’ command to set the current setpoint to 0 and resume normal operation.


Returned in response to a ‘version’ command. Reports the current firmware version in dotted-decimal format.