This blog documents focuses on the SCPI functionality of the electronic load that Robert Peter Oakes, jc2048 and Jan Cumps designed.
The interface works with software that can do serial communications on a COM port. This project comes with a LABView driver and 2 proto GUIs. |
SCPI Interface
| SCPI Command | status | SCPI standard | Comment | Example |
|---|---|---|---|---|
| *IDN? | works | Standard SCPI, implemented by library | callsign | THEBREADBOARD,ELECTRONICLOAD,0,01.00 |
| *CLS | check | Standard SCPI, implemented by library | ||
| SYST:ERR? | works | Standard SCPI, implemented by library | ||
| SYST:ERR:COUN? | works | Standard SCPI, implemented by library | ||
| SYST:VERS? | works | Standard SCPI, implemented by library | SCPI Standard version | 1999.0 |
| *RST | works | Standard SCPI, custom implementation needed | reset to a known status. Switch input off and set to constant current mode. Does not alter stored or temporary calibration settings. | |
| *ESE | check | |||
| *ESE? | check | |||
| *ESR? | check | |||
| *OPC | check | |||
| *OPC? | check | |||
| *SRE | check | |||
| *SRE? | check | |||
| *STB? | check | |||
| *TST? | todo | Standard SCPI, custom implementation needed | Test instrument. Currently does nothing | |
| *WAI | check | |||
<read voltage> MEASure:VOLTage:DC? | works | Query the voltage on the voltage sense inputs. | ||
<read current> | todo | |||
<set mode constant current, constant resistance, what have you, ...> [:SOURce]:FUNCtion
values: CURRent RESistance VOLTage POWer | wip | set the constant regulation mode | On reset, always constant current At this time supports constant current | FUNC CURRent FUNC RESistance FUNC VOLTage FUNC POWer |
| [:SOURce]:FUNCtion? | wip | get the constant regulation mode | At this time supports constant current | FUNC? |
[:SOURce]:INPut[:STATe] <b> | works | Set the input state to ON or OFF | INP ON INP OFF | |
| [:SOURce]:INPut[:STATe]? | works | Query the input state | INP? | |
| <limits> | todo | |||
| DEVElop:DAC# <16 bit value> | works for DAC1 | Development low level | Send the passed value to the DAC. Currently only for the first DAC | DEVE:DAC1 2000 DEVE:DAC1 #H4000 |
DEVElop:ADC#? DEVElop:ADC#:RAW? DEVElop:ADC#:VOLTage? | works for ADC1 | Development low level | Retrieve the last buffered ADC value. Currently only for ADC 1 - 3 | DEVE:ADC1? DEVE:ADC2:RAW? DEVE:ADC3:VOLT? |
| [:SOURce]:CURRent[:LEVel][:IMMediate] | works | Constant Current Mode | Currently accepts RAW DAC value instead of a voltage | CURR 5 |
| [:SOURce]:CURRent[:LEVel][:IMMediate]? | works | Retriev@e the set current level | CURR? | |
| [:SOURce]:VOLTage[:LEVel][:IMMediate] | todo | Constant Voltage Mode | WIP. Mode not implemented yet | VOLT 2 |
| CALibrate | wip | Calibration and Configuration | documented here: Programmable Electronic Load - Calibration Steps | |
For ref: this is what typical instrument (DMM) commands look like We may want to check the commands of a few existing loads, to see if there's a pattern or standard |
|---|
/* DMM */
{.pattern = "MEASure:VOLTage:DC?", .callback = DMM_MeasureVoltageDcQ,},
{.pattern = "CONFigure:VOLTage:DC", .callback = DMM_ConfigureVoltageDc,},
{.pattern = "MEASure:VOLTage:DC:RATio?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:VOLTage:AC?", .callback = DMM_MeasureVoltageAcQ,},
{.pattern = "MEASure:CURRent:DC?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:CURRent:AC?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:RESistance?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:FRESistance?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:FREQuency?", .callback = SCPI_StubQ,},
{.pattern = "MEASure:PERiod?", .callback = SCPI_StubQ,}, |
Error Handling
SCPI
good example: https://github.com/eez-open/psu-firmware/tree/master/eez_psu_sketch, in particular https://github.com/eez-open/psu-firmware/blob/master/eez_psu_sketch/scpi_user_config.h
Complete list: SCPI Errors
e.g.: this can be used to report an invalid function call (set constant voltage value when in constant current mode, ...):
-221 | std_settingsConflict | Settings conflict - Indicates that a legal program data element was parsed but could not be executed due to the current device state. |
catch in the SCPI interface:
missing parameter
parameter out of bounds
index out of bounds
- a non-implemented ADC channel:
DEVE:ADC5? SYST:ERR? -131,"Invalid suffix"
- a missing DAC value:
DEVE:DAC2 SYST:ERR? -109,"Missing parameter"
- more than 16 bits to the DAC:
DEVE:DAC1 66666 SYST:ERR? -224,"Illegal parameter value"
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