C167CS datasheet(223/517 Pages) INFINEON

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C167CS

Derivatives

The External Bus Interface

User’s Manual

9-35

V2.0, 2000-07

Connecting Bus Masters

When multiple bus masters (C167CSs or other masters) shall share external resources

a bus arbiter is required that determines the currently active bus master and also

enables a C167CS which has surrendered its bus interface to regain control of it in case

it must access the shared external resources.

The structure of this bus arbiter defines the degree of control the C167CS has over the

external bus system. Whenever the C167CS has released the bus, there is no way of

actively regaining control of it, besides the activation of the BREQ signal. In any case the

C167CS must wait for the deactivation of its HOLD input.

Note: The full arbitration logic is required if the “other” bus master does not automatically

remove its hold request after having used the shared resources.

Figure 9-14

Principle Arbitration Logic

Compact Two-Master Systems (Master/Slave Mode)

When two C167CSs (or other members of the C166 Family) are to be connected in this

way the external bus arbitration logic (normally required to combine the respective

output signals HLDA and BREQ) can be left out.

In this case one of the controllers operates in Master Mode (the standard default

operating mode, DP6.7 = ‘0’), while the other one must operate in Slave Mode (selected

with DP6.7 = ‘1’). In this configuration the master-device normally controls the external

bus, while the slave-device gets control of it on demand only. In most cases this requires

that (at least) the slave-device operates out of internal resources most of the time, in

order to get an acceptable overall system performance.

MCA04369

Bus Arbiter Logic

C167CR or

other Master

C167CR or

other Master

C 67CR or

other Master

HOLD

HLDA

BREQ

External Bus System

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