CD1865 Datasheet, PDF (43/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

Intelligent Eight-Channel Communications Controller — CD1865
Figure 13. Interrupt Code Sequence
INTERRUPT OCCURS
READ REQUESTING CHANNEL NUMBER
ENTRY POINT FOR
GOOD DATA INTERRUPT
SERVICE ROUTINE
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
5.5.6
IF
N
LOOP COUNTER = 0
Y
SAVE POINTER
EXIT ISR
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.
Datasheet
43