# External extension Interfaces

URL: https://irs.systems/en/docs/messy/external-extension-interfaces

## Supply current measurement – CMM-Interface

For measurement of the DUT current consumption an external IRS current measurement module (CMM) can be inserted. The module is supplied externally and can be read by means of a synchronous serial channel with LVDS differential digital signalling.

The serial interface is designed in a way to concatenate several CMM’s in a daisy chain type, as illustrated in the following figure, where the test system is actually the LVDS interface, which is available on the base and communication board.

![Daisy chain of CMM A, B and C: test system sends Clk_In, En_In, Rx; each CMM forwards Clk_Out, En_Out, Tx; receive data of 3x CMM when asserting En for 3x32 clock cycles, starting with data of CMM C](/docs/assets/messy/images/messy-cmm-daisy-chain.png)

### Communication protocol

The protocol for reading data of one current measurement module is as follows:

![Timing of Clk_In, En_In, Rx and Tx: current bits 31 to 0 sent in two 16-bit blocks with a pause of more than 5 µs between them, followed by the forwarded Rx bits](/docs/assets/messy/images/messy-cmm-protocol.png)

When *En_In* is asserted, the CMM_II module sends out its current measurement value during the next 32 clock cycles with MSB first. After every 16th clock cycle a pause of approx. 5µs with *CLK_In* at low level should be left. This delay is used to leave the CMM_II microcontroller time to sort next 16-bit data word. After 32 clock cycles the previously received data word is forwarded by the CMM.

Thus, *En_in* must be valid for 32 clock cycles, multiplied by number of CMMs in the chain.

The current is returned as 32 Bit unsigned long value in steps of 100nA.

### Connection Diagram

The connection of the signals is according to the following table:

| MesSy signal | MesSy Pin | CMM_II Signal | CMM_II Pin | Which CMM_II |
| --- | --- | --- | --- | --- |
| LVDS_Out_3+ | B16 | Rx+ | B17 | First in chain |
| LVDS_Out_3- | C16 | Rx- | C17 | First in chain |
| LVDS_Out_2+ | B15 | En_In+ | B16 | First in chain |
| LVDS_Out_2- | C15 | En_In- | C16 | First in chain |
| LVDS_Out_1+ | B14 | Clk_In+ | B15 | First in chain |
| LVDS_Out_1- | C14 | Clk_In- | C15 | First in chain |
| LVDS_In_1+ | C12 | Tx+ (last CMM) | B18 | Last in chain |
| LVDS_In_1- | B12 | Tx- | C18 | Last in chain |

Following example shows the connection of the communication lines of two CMMs:

![Wiring example of two CMMs (CMMII_DUT1 and CMMII_DUT2) to the MesSy connector X1 via VG_24+8 connectors, 0,5 mm² wires for supply and LVDS lines](/docs/assets/messy/images/messy-cmm-connection.png)

## Analog or digital output conditioning

For conditioning of digital outputs or using analogue outputs, please refer to document `LDSA_MesSy_Guide_HW_V_1_1.docx`

## External CAN or serial transceivers

For conditioning of digital outputs refer to document `LDSA_MesSy_Guide_HW_V_1_1.docx`

## Analog input conditioning

For conditioning of analog inputs using voltage dividers or load current measurements, please refer to document `LDSA_MesSy_Guide_HW_V_1_1.docx`, and the data sheet `CurrentConverter_8x_Datasheet_V1.0.pdf`.

## External I2C-interface

MesSys with a base- and communication board of version 1.3 or higher provide an external I²C-interface to connect additional external electronic modules. Any devices compatible to the I²C-specification may be connected to this interface.

At the moment IRS provides two external modules, which can be controlled by this interface:

- 64x Relay board (identical to one Relay subsystem on MesSy’s digital output board)
- 16x analogue output board (output DC voltages 0…20V)

I²C-interface contains two signal lines. The signals are available at MesSy connector X2 according to the table in [chapter 2.7.6](/en/docs/messy/hw-description#pinning-vg-connector-x2-power-supply-microcontroller-flashing-reserved) with the following functionality. A typical I²C example telegram for controlling digital outputs is shown in [chapter 3.4](/en/docs/messy/measurement-system-internal-interfaces#digital-output).

| Signal | X2- Pin | Description |
| --- | --- | --- |
| SCL_Ext | B23 | clock line |
| SDA_Ext | C23 | bidirectional data line |