The objectives of this problem are (1) to use a single-chip embedded 9S12 with its ADC to measure force at various locations on a robot and (2) to transmit the measurements across a master/slave distributed network. The robot system will have multiple slaves, each with its own force-measuring circuitry (Figure 12.60). You will design the slaves and specify/implement the communication channel to the master. The force measurement range is 0 ≤ F ≤ 200 dynes. The desired force resolution is 1 dyne. The signals of interest are 0 to 10 Hz. Each slave has +5, +12, and -12 V power. The force transducers are placed in a resistance bridge powered by the +5 V supply (Figure 12.61). The bridge output has a sensitivity of 0.05 mV/dyne. The bridge output is almost zero when the force is zero. This transducer offset for each slave is a constant within the range from 0 to 0.2 mV. Each slave will require a no-force calibration that you will decide whether to handle in software or hardware.
Figure 12.60
Figure 12.61
a) Show the analog interface between the bridge and the 9S12 ADC channel 1. Choose the appropriate op amp circuit, gain, offset, and analog filter. Include a mechanism to calibrate if you decide to handle the offset adjustment in hardware.
b) Design the distributed network between the slaves and their master. All slaves have identical network connections. To get a measurement from one of the slaves, the master will transmit the slave address that should activate exactly one slave. The slave will respond with the current force with a resolution of 1 dyne. The first priority of your network is to minimize cost (i.e., fewest wires and interface chips). Given the cheapest network, the second priority is to maximize bandwidth. Clearly show whether or not the grounds are connected between the multiple computers.
b1) Show the hardware interface between a single-chip 9S12 slave and the network. Remember that the hardware for all slaves will be identical. There is no noise interference.
b2) Show an example communication between the master and a single-chip 9S12 slave. Clearly identify the slave address, and force data components. Label the time axis.
c) Include all of the software that will exist in each slave. Your solution will be segmented into three parts: RAM, EEPROM, and ROM. Specific software requirements include the following:
Other than a one-time initialization, there will be no foreground (main) program
You may use the 9S12 ADC continuous scan mode
Clearly show where the 9S12 is to begin execution on a power on reset
Include a mechanism to calibrate if you decide to handle the offset adjustment in software
c1) Show the software that goes in the RAM (uninitialized on power up).
c2) Show the software that goes in the EEPROM (nonvolatile, but can be different for each slave).
c3) Show the software that goes in the ROM (nonvolatile, and must be the same for each slave).