SPECIAL ENVIRONMENT 80960CA-25, -16
Table 3. 80960CA Pin DescriptionÐExternal Bus Signals (Continued)
Name Type Description
READY I READY is an input which signals the termination of a data transfer. READY is
used to indicate that read data on the bus is valid or that a write-data transfer
S(L)
has completed. The READY
signal works in conjunction with the internally
H(Z)
programmed wait-state generator. If READY
is enabled in a region, the pin is
R(Z)
sampled after the programmed number of wait-states has expired. If the
READY
pin is deasserted, wait states continue to be inserted until READY
becomes asserted. This is true for the N
RAD,NRDD,NWAD
and N
WDD
wait
states. The N
XDA
wait states cannot be extended.
BTERM I BURST TERMINATE is an input which breaks up a burst access and causes
another address cycle to occur. The BTERM
signal works in conjunction with
S(L)
the internally programmed wait-state generator. If READY
and BTERM are
H(Z)
enabled in a region, the BTERM
pin is sampled after the programmed number
R(Z)
of wait states has expired. When BTERM
is asserted, a new ADS signal is
generated and the access is completed. The READY input is ignored when
BTERM
is asserted. BTERM must be externally synchronized to satisfy
BTERM
setup and hold times.
WAIT O WAIT indicates internal wait state generator status. WAIT is asserted when
wait states are being caused by the internal wait state generator and not by
S
the READY
or BTERM inputs. WAIT can be used to derive a write-data
H(Z)
strobe. WAIT
can also be thought of as a READY output that the processor
R(1)
provides when it is inserting wait states.
BLAST O BURST LAST indicates the last transfer in a bus access. BLAST is asserted
in the last data transfer of burst and non-burst accesses after the wait state
S
counter reaches zero. BLAST
remains asserted until the clock following the
H(Z)
last cycle of the last data transfer of a bus access. If the READY
or BTERM
R(0)
input is used to extend wait states, the BLAST
signal remains asserted until
READY
or BTERM terminates the access.
DT/R O DATA TRANSMIT/RECEIVE indicates direction for data transceivers. DT/R
is used in conjunction with DEN to provide control for data transceivers
S
attached to the external bus. When DT/R
is asserted, the signal indicates that
H(Z)
the processor receives data. Conversely, when deasserted, the processor
R(0)
sends data. DT/R
changes only while DEN is high.
DEN O DATA ENABLE indicates data cycles in a bus request. DEN is asserted at the
start of the bus request first data cycle and is deasserted at the end of the last
S
data cycle. DEN
is used in conjunction with DT/R to provide control for data
H(Z)
transceivers attached to the external bus. DEN remains asserted for
R(1)
sequential reads from pipelined memory regions. DEN
is deasserted when
DT/R
changes.
LOCK O BUS LOCK indicates that an atomic read-modify-write operation is in
progress. LOCK
may be used to prevent external agents from accessing
S
memory which is currently involved in an atomic operation. LOCK
is asserted
H(Z)
in the first clock of an atomic operation and deasserted in the clock cycle
R(1)
following the last bus access for the atomic operation. To allow the most
flexibility for memory system enforcement of locked accesses, the processor
acknowledges a bus hold request when LOCK
is asserted. The processor
performs DMA transfers while LOCK
is active.
HOLD I HOLD REQUEST signals that an external agent requests access to the
external bus. The processor asserts HOLDA after completing the current bus
S(L)
request. HOLD, HOLDA and BREQ are used together to arbitrate access to
H(Z)
the processor’s external bus by external bus agents.
R(Z)
10