Consider a communication line modem connected to a computer through an RS-232-C interface. The control signals associated with this interface are accessed by the computer through a 16-bit register, as shown in Figure P10.1. The status change bit, bis, is set to 1 whenever there is a change in the state of bits b12 or b13, or when b4 is set to 1. Bit bis is cleared whenever this register is accessed by the processor. Write a program for one of the processors in Chapter 3 to implement the control sequence required to establish a telephone connection according to steps 1 through 4 of Figure 10.7.LO1

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Status change Data ready CB CA b15 b14 b13b12 by b b CE CF CD Figure P10.1 Organization of an I/O register for the modem interface in Problem 10.6.