1. The Intel486 Processor Basic Bus Cycle D.Geneus 11/23/1996

2. Topics Basic Operation of the 486 Processor Basic Microcomputer System with Input/Output(I/O) Ports and Peripherals Physical Memory and IO space Basic 486 Processor Read Bus Cycle Basic 486 Processor Write Bus Cycle References

3. Basic Operation of the 486 Processor The Intel 486 Processor is a device that executes a program (list of instructions) by repeatedly cycling through the following basic steps: 1. Fetch the next instruction from memory 2. Read an operand if required by the instruction. An operand is a quantity to be operated on as directed by its asscotiated instruction. 3. Execute the instruction (do what the instruction says) 4. Write the result back into memory ( if required by the instruction)

4. Basic Microcomputer System with Input/Output(I/O) Ports and Peripheral REAL TIME CLOCK PROG TIMER PROG INTERRUPT CONTROL DRAM BIOS EPROM FPGA 1. chip select generation 2. byte swap operation 3. state machines 4. ready signal 486 CPU DATA BUS CONTROL BUS ADDRESS BUS 32 10 32

5. Physical Memory and IO space NOT Accessible 64K byte 00000000H 0000FFFFH I/O Space Physical Memory 4G byte FFFFFFFFH 00000000H Physical Memory Space 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 1110 9 8 7 6 5 4 3 2 1 0 byte 1byte 2byte 3byte 4 32 Bit wide Organization highest addressed byte lowest addressed byte

6. Basic 486 Processor Read Bus Cycle valid address valid data read strobe ready TiT1T2T1T2 CLOCK 33 MHz ADSN ADDRESS WRITE/READ DATA READY

7. Basic 486 Processor Write Bus Cycle valid address valid data write strobe ready TiT1T2T1T2 CLOCK 33 MHz ADSN WRITE/READ DATA READY ADDRESS

8. Digital Fundementals, fourth edition, Floyd Intel Military Products data book 1996 - 1997 Local Representative: Zues Electronics 25 Uptown drive Wilmington, Ma 01887 Tel: 508-658- 4776 or 1-800- 524- 4735 Fax: 508- 694-2199 References