C167CS datasheet(222/517 Pages) INFINEON

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C167CS

Derivatives

The External Bus Interface

User’s Manual

9-34

V2.0, 2000-07

Exiting the Hold State

The external bus master returns the access rights to the C167CS by driving the HOLD

input high. After synchronizing this signal the C167CS will drive the HLDA output high,

actively drive the control signals and resume executing external bus cycles if required.

Depending on the arbitration logic, the external bus can be returned to the C167CS

under two circumstances:

• The external master does no more require access to the shared resources and gives

up its own access rights, or

• The C167CS needs access to the shared resources and demands this by activating

its BREQ output. The arbitration logic may then activate the other master’s HOLD and

so free the external bus for the C167CS, depending on the priority of the different

masters.

Note: The Hold State is not terminated by clearing bit HLDEN.

Figure 9-13

External Bus Arbitration, Regaining the Bus

Note: The falling BREQ edge shows the last chance for BREQ to trigger the indicated

regain-sequence. Even if BREQ is activated earlier the regain-sequence is

initiated by HOLD going high. BREQ and HOLD are connected via an external

arbitration circuitry. Please note that HOLD may also be deactivated without the

C167CS requesting the bus.

MCD02236

Other

Signals

CSx

BREQ

HLDA

HOLD

C167CS Datasheet(PDF) 222 Page - Infineon Technologies AG