
AMD
P R E L I M I N A R Y
80
Am79C965
signal, since the internal Buffer Management Unit clock
is a divide-by-two version of the BCLK signal.
The PCnet-32 controller
RDY and RDYRTN signals
may be wired together. This allows the PCnet-32
controller to operate within a system that has a single
READY signal.
The
LDEV signal is generated in response to a valid
PCnet-32 controller I/O address on the bus together
with a valid
ADS signal. LDEV is generated in an asyn-
chronous manner by the PCnet-32 controller. See the
parameter listings for delay values of the
LDEV signal.
RDY, BRDY and D[31:0] are never driven until the sec-
ond T2 state of a slave access. Before that time, it is
expected that a system pull-up device is holding the
RDY and BRDY signals in a deasserted state.
The
RDY and BRDY signals are always driven high for
one half BCLK cycle immediately following the BCLK
period during which
RDY was driven asserted. Then the
RDY and BRDY signals are floated. This behavior is
performed regardless of the PCnet-32 controller mode
setting. See Figure 25.
18219B-28
ADS
Ti
BCLK
T1
T2
ADDRESS,
BE0-BE3,
M/
IO,
D/
C
RDY
W/
R
BRDY
D0-D31
T2
T2x
Ti
From
PCnet-32
LDEV
Valid
Not Valid
RDYRTN
Figure 25. Slave RDY Timing
VESA VL-Bus Mode Timing
VESA VL-Bus mode functional timing is essentially
identical to the timing of the Am486 32-bit mode, except
that the bus request and bus acknowledge signals have
inverted senses from those shown in the previous timing
diagrams and the AHOLD signal does not exist while the
PCnet-32 controller is programmed for VL-Bus mode. In
addition, dynamic bus sizing is supported in VESA VL-
Bus mode, through the use of the
LBS16 signal. The
following section describes possible
LBS16 interactions
while programmed for the VESA VL-Bus mode of
operation. Other differences exist between VL-Bus
mode and Am486 mode, but these other differences are
not directly related to the master or slave cycle timings.
Effect of LBS16 (VL-Bus mode only)
Dynamic bus sizing is recognized by the PCnet-32 con-
troller while operating in the VL-Bus mode. The
LBS16
signal is used to indicate to the PCnet-32 controller
whether the VL-Bus target is a 16-bit or 32-bit periph-
eral. When the target device indicates that it is 16 bits in
width by asserting the
LBS16 signal at least one LCLK