What is the difference between static and global variables?

– Answer the following questions in a couple of sentences. [30 pts, 6 pts each]
• What is the difference between static and global variables?
• If you are severely limited by the physical space of the microcontroller you were asked to
design, would you choose Harvard or Von Neumann architecture?
• What is the advantage of RISC over CISC?
• What can go wrong if the BAUD rates of the sender and the receiver do not match?
• What does it mean to have an 8-bit processor? In other words, what does 8-bit signify in
such a system?
• They both represent variables that have a static location in memory. The main difference
is the scope of the variable. The scope of static variables (defined with the “static”
keyword) is a function whereas global variables are accessible by any function in a .c file.
• If you are severely limited in terms of space, Von Neumann architecture might be better
as it has a single memory unit for data and instruction memory.
• RISC instructions are shorter and simpler, thus requiring less complex hardware and each
instruction can complete very fast.
• There might be missing bits or unnecessarily repeating bits (data corruption) depending
on whichever side has higher/lower BAUD rate.
• It means that each address location holds 8 bits, including memory locations and
registers. Example: in your AVR device each register hold 8 bits of data.

3 – Serial I/O [40 pts]
Assume that we have the following USART module description on an 8-bit microcontroller:
• The USART module has two 8-bit registers: status register and data register.
• We have a variable, named USART_SR, to represent the status register.
• We have a variable, named USART_DR, to represent the data register.
• The individual bits of the status register (UART_SR) are designed as follows:
7th bit 6th bit 5th bit 4th bit 3rd bit 2nd bit 1st bit 0th bit
RBE – – TBF – –
• RBE bit (“Receive Buffer Empty”) is set to 1, when the receive buffer is empty, and to 0,
whenever the receive buffer is full, i.e. the received character is in the data register.
• TBF bit (“Transmit Buffer Full”) is set to 1, when there is unsent data in the transmit buffer
and to 0, when transmit buffer is empty, i.e. it is okay to write a new character to the data
register.
• USART_DR register works similar to the one in your AVR device, i.e. reading this register
means receiving a character from USART and writing to this register means transmitting a
character via USART. However, you need to make sure that appropriate buffer conditions
are in place before using this register (USART_DR).
Using the above description, write down a function, using the prototype below, that does the
following:
i. It continuously receives a character through serial I/O.
ii. It waits for 50 ms after receiving a character. You can assume that there is a
delay_ms function with the following prototype:
delay_ms(int time)
iii. If the received character is a lowercase letter, it converts it to uppercase and
transmits the converted character through serial I/O.
iv. If the received character is a numerical character, i.e. if the received character
belongs to {‘0’, ‘1’, ‘2’, ‘3’, ‘4’, ‘5’, ‘6’, ‘7’, ‘8’, ‘9’}:
a) It transmits ‘0’ through serial I/O, if the numerical character represents an
even number.
b) It transmits ‘1’ through serial I/O, if the numerical character represents an
odd number.
v. It waits for another 50 ms if there is a transmission.
vi. It does not transmit anything through serial I/O, if the received character does not
belong to the groups mentioned in iii and iv.
You can assume that the USART module is initialized in some other part of the main code
(e.g. the BAUD rate, data frame properties, etc.). Regarding USART, you are only
responsible for implementing receive and transmit functionalities in the function below.