2.1 Basic Components

The main components and external interfaces of the ADS Controller/Driver are described below.

2.1.1 Processor RTX2010

The RTX2010 processor from Harris is a powerful radiation hardened 16-bit micro-controller with a stack oriented multiple bus architecture. Its natural machine language is Forth. A clock frequency of 1.7152 MHz was chosen for the processor, which is a good compromise between performance and power consumption.

2.1.2 Memory

The Controller Board is prepared to be equipped with 16 kByte PROM/EEPROM (2 $\cdot$ 8 k) and 64 kByte (2 $\cdot$ 32 k) of static RAM. After system reset the application code located in the PROM is copied into RAM and then executed from there. The PROMs are switched off after the code download to RAM, which leads to a lower power consumption because RAMs in general need less power than PROMs. The other advantage is that the operating system can use a straight RAM model. System variables, interrupt tables, system software is located in RAM and can be changed and/or extended at run-time (or interactively).

2.1.3 FPGA

The 8000 gate Actel A1280A FPGA integrates all the logic needed for the ADS Controller (except the Schmitt-Trigger circuit for the power-up reset):

• control signals generator for memory and I/O access
• power-up reset logic
• clock generator
• address decoder
• watchdog circuit
• CDMS Interface
• CDMS housekeeping and data registers
• ADS control Register
• interface for a 12 bit ADC and a 8 channel multiplexer
• security mechanisms for the valve and tank-opener control lines

2.1.4 CDMS Interface Driver

As it is advised in the CDMS-REID-A document, the Controller uses a CD4050B device and the proposed resistor configurations for buffering the CDMS main and redundant signals.

2.1.5 Analog-Digital Converter

The Analog-Digital Converter (ADC) is on the Controller Board. It is an AD1671 from Analog Devices. Input range is 0 to 2.5 V, the resolution is 12 bit, conversion time is about 800 ns, it has a built in sample and hold circuit.

2.1.6 Multiplexer

There is a 8 channel analog multiplexer on the Controller Board. It is an DG508ACJ from Harris. The multiplexer enable line is tied to VCC, the multiplexer is always enabled.

Table 1: Analog Multiplexer

Channel	Description
1	acceleration
2	tank pressure
3	pipe pressure
4	+5 V power supply current
5	+12 V power supply current
6	+28 V power supply current
7	-5 V power supply current
8	-12 V power supply current

2.1.7 Level Shifter

There is a level shifter for the accelerometer. It adds 250 mV to the acceleartion signal, because the ADC can convert only positive signals.

There are also two voltage dividers for the pressure signals. The pressure signals are divided by two.

For the current measurements there is no level shifting needed. The signals from the Electronic Interface Board are tied direct to the analog multiplexer.

2.1.8 Power Driver

There are 4 power drivers for the valves and the tank opener actuators. They have to drive about 0.8 A for each actuator. Only one actuator is active at the same time. Two ULN2003A are used as power driver. For every output 3 driver stages are in parallel.

2.1.9 Current Measurement +28 V

The current measurement circuit is very similar to the citcuits used on the Electronic Interface Board. The ADS QM is using a MAX472 too.