QUESTION $1$

$[25]$

The following AVR program is a student's counter that counts the number of students in a class room and displays on a remote unit with a USART interface running HyperTerminal. Only one person can enter and exit at a time. The initially empty class room has a maximum capacity of $99$ students, one entry and one exit point equipped with entry and exit sensors that generate a LOW when activated. The code shown in Figure Q$1$ below is not complete. Assume all the registers are defined.

The ATmega $32$ parameters are as follows: A $8MHz$ clock. USART baud rate of $1200bps,$ one start bit, $8$ data bits, no parity and one stop bit. The code is not complete. Assume all the registers are defined.

a$)$ Draw a block level schematic diagram representing the modules required to build the system, their functions and how they are interconnected including the remote unit. Indicate the pin connections used and the reason for the choice.

$6$

b$)$ Determine the hexadecimal values missing at the following:

$4$

i$.)$ Line $3.$

ii$.)$ Line $5.$

c$)$ Write the code to be placed at the following:

$9$

i$.)$ Line $9,$ configuring the interrupts.

ii$.)$ Line $10,$ configuring the USART protocol.

iii.$)$ Line $16$ and Line $19.$

d$)$ What would happen if Line $17$ is omitted?

$[2]$

e$)$ What could be wrong with Line $24?$ How would you correct the problem?

$4$

Note: In all cases show the working.

$\backslash$table$[[\mathrm{.}0rg000,$;Line $1],[$rimp Init,;Line $2],[.$ org $0$xdots....,;Line $3],[$rimp INTO$\_$ISR,;Line $4],[org0$xdotsF,;Line $5],[$rimp INT$1\_$ISR,;Line $6],[.$org $0100,$;Line $7],[$Initstack$,$;Line $8],[$;configure Interrupts,:Line $9],[$;configure USART,;Line $10],[$Idi Num$\_$Stds$,$ Ox$...,$;Line $11],[$Start:$,$;Line $12],[$rcall transmit,;Line $13],[$jjmp Start,;Line $14],[$INTO$\_$ISR:,;Line $15],[$;process line,;Line $16],[$reti$,$;Line $17],[$INT$1\_$ISR:,;Line $18],[$;process line,;Line $19],[$reti$,$;Line $20],[$TRANSMIT:$,$;Line $21],[$sbis UCSRA, UDRE,;Line $22],[$rjmp TRANSMIT,;Line $23],[$out UDR, Num$\_$Stds$,$;Line $24],[$ret$,$;Line $25]]$

Figure Q$1$