Microprocessors 1. History of Intel Processors. First microprocessor ~ Intel 4004 4-bit (nibble) data bus; contained 2000 transistors; 46 instructions; 4 KB of instruction code and 1KB of data Second generation (1974) ~ Intel 8008, 8080, 8085
(1 MB of memory); capable of handling 8 or 16 data bits at a time; 8088 is a stripped down 8-bit external data bus version
Improved 80386DX with on-chip memory cache and math co-processor
Enhancement of the P-5; bus structure supports up to four processors; speeds >= 300 MHz; efficient power usage; P-6 bus detects and correct all single-bit and multi-bit bus errors.
Address is strobed from external latch (8282, 82C82) when ALE (Address Latch Enable) goes from high; data is latched when ALE pulses from low; ALE oscillates with regular clock cycle; the process of switching between data and addressing is called demultiplexing.
Additional 8086/88 pins:
Status pin functionality- continued
Additional pin functionality:
VCC/GND: power (5 and 0V)
MN/MX: 0/1 ~ MIN or MAX mode
BHE: Bus High Enable ~ enables the most significant data bus bits (D15-D8) during a read or write operation