Read bus cycle timing Diagram in Minimum Mode

Draw and explain the Read Bus Cycle in Minimum Mode System Configuration of 8086 Microprocessor

Read Bus Cycle in Minimum Mode of 8086 Microprocessor: The 8086 microprocessor can operate in two modes, Minimum mode and Maximum mode. In minimum mode, the 8086 microprocessor functions as the sole processor in a system, utilizing a straightforward configuration with a single 8-bit data bus and a 20-bit address bus. This simplicity comes at the cost of limiting its potential performance. Let’s delve into the details of the Read bus cycle in minimum mode, making it relatable with a real-world example.

Read Bus Cycle in 8086 Minimum Mode:

The Read bus cycle in the 8086 microprocessor’s minimum mode is a crucial operation where the processor fetches data from memory. Spanning four clock cycles (T1, T2, T3, T4 State). The Read bus cycle in 8086 minimum mode is like fetching a specific item from a shelf. The 8086 processor signals the item’s location (address), the shelf is checked, and the item (data) is picked up and noted. It takes four steps, and while it’s simple, using only an 8-bit bus can slow things down a bit. Think of it like shopping for groceries – you tell the store where to find something, they check the shelf, grab the item, and you’re ready to go!

  • T1 State:
    • The 8086 puts forth the address on the 20-bit address bus.
    • ALE (Address Latch Enable) rises, indicating that the address is valid and can be latched externally.
    • I/O M’ drops, indicating a memory read operation.

Real-World Example: T1 State (Traffic Light Changes):

  • The traffic controller (8086) signals a valid address to vehicles (data).
  • A green light (ALE) allows vehicles to proceed for a memory read.
  • T2 State:
    • ALE lowers.
    • BHE (Bus High Enable) and A0 signals are asserted to discern if the address points to the high-order byte, low-order byte, or both bytes of a 16-bit word.

Real-World Example: T2 State (Traffic Lane Identification):

  • The traffic controller changes the lights based on the type of vehicles (BHE/A0).
  • Identifying whether it’s a two-wheeler (low-order byte), a car (high-order byte), or a bus (both bytes).
  • T3 State:
    • The memory device reads data based on the address and BHE/A0 information.

Real-World Example: T3 State (Vehicle Movement):

  • Vehicles (data) move through the road (addressed memory location), and each type of vehicle collects relevant information (BHE/A0).
  • T4 State:
    • Data is placed on the 8-bit data bus.
    • The 8086 internally latches the data.

Real-World Example: T4 State (Data Arrival):

  • Vehicles (data) reach their destination on the road (8-bit data bus).
  • The traffic controller (8086) internally notes the information.

Important points to note:

  • The entire Read bus cycle takes four clock cycles (T-states).
  • The 8086 outputs all the necessary control signals for memory access in minimum mode.
  • This mode is simpler to implement but limits the system’s performance due to the single 8-bit data bus.