Processor

Shown below is the payload computer motherboard.  The board contains the processor as well as the power converter, analog and digital I/O, and TNC MODEM.  The processor is a Z-World micro controller module board.  The board includes the processor, clocks, flash memory, battery backed SRAM, and programming port on a single 1.9" x 2.3" x 0.5" (48.3 x 58.4 x 12.7 mm) board.  Surface mount components are on both sides on the board.



Payload Computer Motherboard.


Features

All I/O through connectors to allow for ease of upgrades and repairs.

Industrial temperature range, -40° C to° C.

High efficiency power converter.  Heat sink not required.  Provides multiple output voltages (+3.0, +3.8, and +5.0 VDC) for subsystems.

256K flash memory, 512K battery backed SRAM.  Battery backup to maintain logged data, system parameters, and GPS almanac/ephemeris data.

Buffered serial ports, discrete I/O ports, and programming port.

Standard audio and PTT (Push-To-Talk) interface to radio.

Instrumentation grade, 16-bit ADC (Analog to Digital Converter) for high dynamic range.

On-board temperature sensor.

Software in C programming language


Trade Study

The following other processor were considered:

Motorola 68HC11/12 - The 'HC11 is considered the standard in 8-bit micro controllers.  However, it is showing it age.  The part has limited on board memory and a single serial port.  In addition, the parts are on manufacturer allocation and are difficult to obtain.  The 68HC12 Is an updated version of the 68HC11 with onboard flash memory and additional I/O.  However, the part is only available as a fine pitch surface mount component.

Microchip PIC controller - The PIC controller family is an excellent set of 8-bit parts, however they don't scale well in larger projects that require external memory or have extensive I/O requirements.

Parallax BASIC Stamp Controller - Their BASIC stamp controller is a good choice for small, ground control applications.  However, the products are not specified for operation over industrial temperature ranges, lack I/O capability, don't support real-time interrupts, and lack a structured programming language.