Q1 -(LT2: Basic I/O Mechanisms)[30%]< A smart robotic dog module installed with 8 sensors and associated registers is connected as an input device through an I/O interface board to the MC68HC11 microcontroller. After the microcontroller requests to perform a READ operation on the smart robotic dog module, the ON/OFF status of each sensor (S0 -- S7) represented as 1/0 will be updated to the data buffer register (DBR) of the I/O interface board. S7 will be loaded into the most-significant-bit [MSB] (bit 7) of DBR while S0 will be loaded into its least-significant-bit [LSB] (bit 0) after each update. For instance, if S5 is ON while the remaining sensors are OFF, the updated content of DBR should be: 001000002. For any input device, the control/status register (CSR) and DBR of the I/O interface board is assigned to memory address $8004 and $8008 respectively. The command code to perform a READ operation on the smart robotic car module is $3A.
(a) Clearly explain the detailed steps with an illustrative diagram to load 1 byte of data from the DBR of the I/O interface board to the Accumulator A of the MC68HC11 microcontroller using the programmed I/O mechanism while the Accumulator B is used to load the command code. (22%)
(b) Assume sensors S7, S4, S2, and S1 are ON and the remaining are OFF at the moment after applying the programmed I/O mechanism described in (a), what are the resulting contents of Accumulator A and B? (8%)