CD1865 datasheet(43/150 Pages) INTEL

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Intelligent Eight-Channel Communications Controller — CD1865

Datasheet

5.5.6

Cascading Service Requests with Multiple CD1865s

Regardless of the method used to support service requests, multiple CD1865s can be cascaded by

tying together all * lines, all * lines, and * lines. These lines are open-drain so they may be wire-

OR’ed. The CD1865s are then daisy chained by simply connecting the ACKOUT* of one device to

the ACKIN* of the next.

The host knows which CD1865 is requesting service by the ID value returned through the Global

Interrupt Vector register. Up to 32 CD1865s can be cascaded in any one daisy chain in this manner.

Since multiple daisy chains are possible, the maximum number of CD1865s can be large. The 32-

per-daisy-chain limit is set by the five bits in the GVR. These bits can be used to identify which

CD1865 responded to the service request acknowledge cycle. The user must program different

values into the upper-five bits of each CD1865s GVR.

Figure 13. Interrupt Code Sequence

INTERRUPT OCCURS

READ REQUESTING CHANNEL NUMBER

READ NUMBER OF BYTES FROM RDCR

SET UP HOST’S BUFFER POINTERS

SET LOOP COUNTER = RDCR

READ RDR

WRITE DATA TO POINTER LOCATION

INCREMENT POINTER

DECREMENT LOOP COUNTER

LOOP COUNTER = 0

SAVE POINTER

EXIT ISR

ENTRY POINT FOR

GOOD DATA INTERRUPT

SERVICE ROUTINE

CD1865 Datasheet(PDF) 43 Page - Intel Corporation