Lab3: BCD Adder Circuit Design
Lab4: Z80 Simulator - Interrupts &
Interrupt Handling
Lab3: BCD Adder Circuit Design
Objectives
1 - Learn BCD representation .
2-Learn addition using BCD.
3-Design circuit that add two packed BCD numbers
and simulate it using Proteus .
• The main points should be revised for Lab
-In BCD, a digit is usually represented by four bits
Which represent the decimal digits 0 through 9 .
-Addition :
1001
9
1000+ 8
Not 0111
1 0 0 0 1 = 17
Need correction
Correction : 1 0001 + 0 0110 = 1 0 1 1 1
Using 4008 ADDER to ADD two BCD digits
-4008 is a 4-bit adder with carry out and carry in .
-Numbers consist of Two BCD digits (packed BCD)
can be added using this adder as follow :
1- Add the first digits in the two numbers
2- connect the carry out of first adder as
carry in to second adder and add
the second digits .
Lab4: Z80 Simulator – Interrupts &
Interrupt Handling
Objectives:
1 - To introduce the concept of interrupts as a means
to perform Input/Output operations
2-To show the different types of interrupts usually
available in microprocessors
3- To demonstrate how interrupts are handled
4- To be familiar with Z80- Simulator software
• The main points should be revised for Lab
-POLLING : Regulary check for an input signal and
respond when it be active .
- INTERRUPT : CPU do other works and When an input
signal is active suspend it’s working and respond .
- Interrrupt is checked regularly at end of each
instrucion
The Z80 microprocessor interrupt lines :
- Non maskable Interrupt “-NMI” : respond to interrupt
for falling edge signal and the programmer cannot
disabled it .
- Interrupr request ”-INT” : respond to interrupt for logic
zero signal and the programmer can disable it .
For interrupt request there is interrupt enable flip flop
“IEFF” that have two status :
Logic one : enable interrupt request using EI instruction.
Logic zero : disable interrupt request using DI instruction
Non maskable Interrupt “-NMI” operation
- when an –NMI occurs from any source Z80
respond as follow:
1- it disable the –INT line .
2- Save current address of PC in stack and also for
registers
3- load the address 0x0066(address of interrupt
service rotuine ) to PC
4- after execution of ISR , return instruction
should be put to return to Main Program .
Interrupt Request “-INT” Operation
- when an –NMI occurs from any source Z80
respond as follow:
1- Save current address of PC in stack and also for
registers
2- load the address 0x0038 (address of interrupt
service rotuine ) to PC
3- after execution of ISR , return instruction
should be put to return to Main Program .
Interrupt Request Modes
MODE 1 : the same as –NMI .
MODE 0 , 2 : discriminating between different
sources of interrupts by accepting an external
data inputs .