CE121L - Microprocessor System Design
Laboratory 4
Week of February 10, 1997

In this laboratory, you will using the serial interface. As you write more and more complex programs, be sure to make your code modular to simplify change and reuse. In particular, use symbolic constants rather than addresses in your code.

Prelab

1. Read section 9 of the HC11 manual. 
2. Read section 9 once more, very carefully. 
3. Carefully consider the setting of every serial interface configuration register. Turn off interrupts (we will use polling to start with), and enable the transmitter and receiver.
4. Decide what settings are required to send data at 1200 baud.
5. Add an initialization program for the UART to your HC11 boot routine. Transmit data with 8 bits, no parity, with one stop bit (see steps 1 and 2).
6. To test the serial I/O, you will be connecting the TxDA and RxDA pins, making the UART receive its own data. Referring to steps 1 and 2, determine how to connect the remaining pins. Do not do the loopback through your level converter.

Laboratory

1. With the read/write loop cycling, observe the TxD line on a scope. Always check the status registers before reading or writing to the UART. Draw a diagram of the scope output for 1 byte of transfer, and confirm your baud rate setting.
2. Connect the RS-232C level converters. RS-232C levels are dangerous to your circuit. Always turn off power when you are changing wiring or, next week, when you are plugging or unplugging the PC's RS-232C cable into your kit. Do not do a loopback between the level-converter's driver and receiver.
3. Extra: Find another group that has gotten to this point and has 8 LEDs or a seven-segment display on their board. Connect your RS232-C output to their input, and vice-versa. Don't forget the third wire in a 3-wire connection. Run your programs that continuously writes a number to the UART. Is it received by the other group?
4. Write a program that will continuously poll the receiver port. Whenever it receives a character, if it an ascii letter, make it an upper case letter and write it out the transmit port as soon as the transmitter is ready. Hook this up to a PC and give it a try.

MSKermit

You will run MSKermit on the PC to emulate a dumb terminal. The appropriate commands within MSKermit are:

set port 2          ; use I/O port 2 on the PC
set baud 1200       ; port 2 to 1200 baud
connect             ; begin VT52 terminal emulation

Output from the keyboard will be sent directly to your HC11, and input to the PC will be sent directly to the screen. Use 1200 baud, 8-bits, no parity when talking to the PC. As a minimum, you should echo characters to the screen to confirm what you have typed.