MECA Common Electronics (MISC)

Instrument Overview

The MECA instrument suite on the Phoenix spacecraft returns 15 distinct unchannelized telemetry types, of which three are common to all the component instruments (microscopes, chemistry laboratories, and thermal and electrical properties probe). These are types 4 (CME_STATUS), 5 (POWER_DATA), and 6 (TABLES).

Type 4 is a direct response from the FPGA that controls all aspects of MECA operations. The most common usage of this telemetry type is as a reply to routine requests including turning on LEDs for imaging, moving the microscope sample stage, deploying a chemistry actuator (sample drawer, water release, or stirring motor), or simply a status inquiry. The data return provides not only confirmation that the requested operation occurred, but specific information necessary for calibration, such as the position of the stage when the atomic force microscope is engaged. A second usage of this telemetry type is in response to a 'raw' command, a direct instruction to the FPGA to execute any of its allowed functions. While not recommended for routine science measurements, this mode is often used for operations that are not performed in the desired sequence by the standard flight software commands. Notably, this may include voltammetry and potentiometry measurements in the chemistry cells, in which case the Type 4 return contains primary science data.

Type 5 data returns the voltage and current provided by the primary MECA 5V (load and logic) and 15V (load and AFM) power supplies. These results are diagnostic of the functioning of all subsystems and should be indicative of many anomalous conditions.

Type 6 data returns, on request, the contents of any of six tables that modify the operation of the MECA flight software (FSW). These include a state table which is autonomously maintained by FSW as well as several tables that can only be set by explicit user command. These user-maintained tables contain the values and allowed ranges of parameters and attributes that define the implementation of each experiment. For microscopy, for example, they might define the different substrate positions on the sample wheel as well as the optimal focus position. Download of these latter tables is for the purpose of confirmation that the actual parameters of an experiment were set as intended.

More information is found in HECHTETAL2008, KOUNAVESETAL2008, and ZENTETAL2008.

Detectors and Electronics

MECA flight software (FSW) runs on the primary spacecraft computer and communicates to MECA hardware at 9600 baud via a serial Payload and Attitude Control Interface(PACI) interface. On the other side of that interface is an FPGA, located on the Command and Measurement Electronics (CME) board inside the MECA enclosure. The FPGA controls all hardware functions in the MECA suite with the exception of the Atomic Force Microscope (AFM), which has an embedded processor, and discreet switches, controlled directly by the spacecraft computer, for powering MECA and for switching between AFM processor and FPGA. Data return described here is generated by the FPGA.

Location on spacecraft

Information described here is returned by the FPGA on the Command and Measurement Electronics (CME) board, which is located inside the MECA enclosure on the spacecraft deck.