![](http://datasheet.mmic.net.cn/350000/CD1865_datasheet_16531773/CD1865_99.png)
Intelligent Eight-Channel Communications Controller
—
CD1865
Datasheet
99
Bit
Description
Bit 7
PkgTyp:
This read-only bit indicates the CD1865 package type. This bit always reads back as .
Bit 6
RegAckEn:
Enables register-based service-request acknowledgments. If this bit is a
‘
0
’
, register-based
acknowledgments are not accepted. In this case, the results of a read of any of the service-acknowledgment
registers are undefined. This is the default state of RegAckEn, and it ensures compatibility with earlier
versions of the CD1865.
When RegAckEn is enabled, register-based acknowledges allow the user
’
s software to acknowledge a
service request by reading from a register rather than by driving the external ACKIN* signal. This is
convenient in applications where interrupts are not supported or where polling is preferred. Setting this bit
does not disable the function of the ACKIN* signal.
Bit 5
DaisyEn:
Enables daisy-chaining of register-based service acknowledgments. When DaisyEn is a
‘
1
’
, a
CD1865 being addressed with a register-based service acknowledgment (a read occurs from a register-
acknowledgment address) for which it has a pending request, places the contents of the Global Interrupt
Vector register modified by the service type on the data bus.
When DaisyEn is a
‘
1
’
, a CD1865 being addressed with a register-based service acknowledgment, for which it
does not have a pending service request, asserts ACKOUT* to pass the acknowledgment down the daisy
chain. The next CD1865 in the chain monitors the acknowledgment as an ACKIN* acknowledgment. The
Service Request Acknowledge register addresses must be placed in the corresponding Service Match
registers (, , and ) as part of the user setup for daisy-chaining of register-based service acknowledgments.
If daisy-chaining of register-based service acknowledgments is not used, the Service Match registers may be
programmed with any address codes that the user finds convenient for use with the
‘
normal
’
ACKIN* service-
acknowledge mechanism.
If DaisyEn is a
‘
0
’
and a CD1865 is addressed with a register-based service acknowledgment for which it does
not have a pending service request, it responds by providing an interrupt vector with a modification code of
‘
000
’
. The addressed CD1865 treats this as an interrupt acknowledge cycle, but with passing inhibited, it must
‘
take
’
the acknowledge with an ACK level of
‘
00
’
(none of the interrupt types).
RegAckEn must be a
‘
1
’
to enable register-based service acknowledgments. DaisyEn has no effect on daisy-
chain operation of the regular ACKIN*/ACKOUT* chain.
Bit 4
GlobPri:
When AutoPri is used, if GlobPri is set to a
‘
1
’
, the CD1865 prioritizes across multiple CD1865s
sharing REQ () lines. If GlobPri is set to a
‘
0
’
, the CD1865 accepts the acknowledge for the highest priority on-
device interrupt. In both cases, automatic prioritizing is only done on type 1 (normally the modem signal
change type) interrupt acknowledgments through the ACKIN* mechanism or the register-based acknowledge
mechanism.
When using GlobPri and AutoPri, it is possible to use the CD1865 with the three REQ lines wire-OR
’
ed
together. In this configuration, with any interrupt request asserted, the global values of all requests appears
asserted. GlobPri should be a
‘
0
’
to force prioritization among the interrupt sources on-device. When no on-
device interrupts are pending, the acknowledgment is subject to daisy-chaining. See DaisyEn description.
Bit 3
UnFair:
Fairness Override bit. If UnFair is a
‘
0
’
, normal Fair Share Interrupt control is performed. If UnFair is a
‘
1
’
, the fair bits are all forced to a
‘
1
’
, disabling the Fair Share mechanism. This is useful when the AutoPriority
Option is used, and the different REQ lines are wire-OR
’
ed together.
Bit 2
Reserved. Must be a
‘
0
’
.
Bit 1
AutoPri:
When set, indicates that the CD1865 should prioritize service requests in the manner selected by
the PriSel bit. In conjunction with the GlobPri bit, either local (within the device) or global (across daisy-
chained devices) prioritization is done. With AutoPri set, auto-prioritization is performed only when a type 1
(modem) interrupt acknowledgment is recognized. Acknowledgments of type 2 (transmit) and 3 (receive)
interrupts continue to be unique and specific even with AutoPri set. This offers a form of local override to Auto-
prioritization for Transmit or Receive Service Request when continuing a second-priority service routine. If not
set, the user must indicate the service request being acknowledged by the choice of service request
acknowledge register.
AutoPri x GlobPri => look at REQext to prioritize globally.
AutoPri x GlobPri* => look at REQ to prioritize locally.
Bit 0
PriSel:
Prioritized interrupt order option. If AutoPri is set, PriSel selects the highest-priority service request. If
PriSel is a
‘
0
’
, receive requests have the highest priority. If PriSel is a
‘
1
’
, transmit requests have the highest
priority. Modem signal change request priority is fixed at the lowest priority.