Signal Interface of 80386DX

1. Signal Interface of 80386DX

2. Signal Interface

3. Signal Interface • Signals are arranged by functional groups. • The # symbol indicates active low signal. • When no # is present, the signal is active high. • Example: M/IO# - High voltage indicates memory selected • - Low voltage indicates I/O selected

4. Signal Interface • Clock (CLK2): • It is divided by two internally to generate the internal processor clock. • The phase of internal processor clock can be synchronized to a known phase. • Data Bus (D0 through D31): • It has three-state bidirectional signals. • It can transfer data on 32- and 16-bit buses using a data bus sizing feature.

5. Signal Interface • Address Bus (A2 through A31) • These three-state outputs provide memory or I/O port addresses. • It can access 4GB of physical memory from 00000000H to FFFFFFFFH • Of the total 32-bits, only higher 30 are released by MP • A1 & A0 are used internally by MP to produce 4 bank enable signals(BE3# - BE0#)

6. Signal Interface • Byte Enable Outputs( BE0# -- BE3#) • enable 4 memory banks • indicates which bytes of the 32-bit data bus are involved with the current transfer. • BE0# applies to D0-D7 • BE1# applies to D8-D15 • BE2# applies to D16-D23 • BE3# applies to D24-D31 • No. of Byte Enables asserted indicates physical size of operand being transferred (1, 2, 3, or 4 bytes).

7. Signal Interface

8. Signal Interface

9. Signal Interface • Bus Cycle Definition Signals (W/R#, D/C#, M/IO# , LOCK#) • three-state outputs • W/R# :distinguishes b/w write and read cycles. • D/C# :distinguishes b/w data and control cycles. • M/IO# :distinguishes b/w memory and I/O cycles. • LOCK# :distinguishes b/w locked and unlocked bus cycles. It enables CPU to prevent other bus masters (like coprocessor) from gaining the control of system bus.

10. Signal Interface • Bus Cycle Definition Signals: These control signals are decoded by the bus control logic to decide which bus cycle to be performed

11. Signal Interface • Bus Control Signals(ADS#,READY#,NA#,BS16#): • indicates when a bus cycle has begun and allow other system hardware to control address pipelining, data bus width and bus cycle termination. • ADDRESS STATUS (ADS#) : indicates that a valid address is driven at 80386DX pins. • TRANSFER ACKNOWLEDGE (READY#) : indicates that the previous bus cycle is complete and bus is ready for next bus cycle. It is useful for interfacing slow peripherals

12. Signal Interface • NEXT ADDRESS REQUEST (NA#) : • This is used to enable address pipelining. • It indicates that the system is prepared to accept the next address even if the end of the current cycle is not being acknowledged on READY#. • BUS SIZE 16 (BS16#) : Asserting this input constrains current bus cycle to use only the lower-order half (D0-D15) of data bus, corresponding to BE0# and BE1#.