Understanding 8086 Microprocessor Development Kit

Look at the following block diagram of 8086 microprocessor development kit carefully.

Following are the individualy physical chips present on the board:

• Intel 8086 Microprocessor chip
• Two EPROM memory chips
• Two Static RAM (SRAM) memory chips
• Programmable Peripheral Interface (PPI) chip 8255A
• USART chip 8251A
• Programmable Interval Timer 8254

8086 CPU

Following are the features of 8086 CPU:

• It is 16 bit CPU, All the registers are 16 bit in size
• 16 Data lines
• 20 address lines
• 8 general purpose registers, 4 Segment registers, Instruction pointer, Flags register
• Variable length CISC instruction set
• Clock speed 8 MHz

CPU has got 16 data lines, so that it can move data between registers and memory in a single cycle. CPU has 20 address lines, so it can address total memory (both EPROM and RAM put together) of 1 Mega Bytes. 8086 CPU supports two types of addresses. One is memory address used to address EPROM and RAM, and second is IO address used to address IO peripheral chips. The 8086 instructions are considered as complex instruction set. Instruction size is variable. Some instrucitons are 1 byte, some are 2 and 3 bytes. Some instructions directly works on memory operands.

EPROM and static RAM chips

You will find two EPROM chips and two SRAM chips. This is because, each memory chip supports only 8 bit locations. By connecting two memory chips in parallel, CPU can transfer 16 bit data, between registers and memory. When CPU is reading or writing 16 bit locations, both the memory chips will be selected at the same time. Lower 8 bits of data will go to the one memory chip and upper 8 bits will go to the second memory chip.

8255, PPI chip

This chip is general purpose digital IO chip. It supports total 24 GPIO pins. These 24 pins are divided into three ports of 8 pins each. By reading or writing to 8 bit port register, we can read or write to the GPIO pins. Search the Internet for '8255 Datasheet', download and read.

8251, USART chip

This supports RS-232 serial communication. Through this port, 8086 kit can be connected to other devices like GSM/GPRS Modem, GPS, Zigbee etc. This port also can be connected to PC and establish communication between PC and 8086 kit. Search the Internet for '8251 Datasheet', download and read.

8254, Timer chip

This chip has got three independent Counters. We can program these counters and can use them in different modes of operation. Search the Internet for '8254 Datasheet', download and read.