
AMD
P R E L I M I N A R Y
20
Am79C965
If
BRDY and RDYRTN are sampled active in the same
cycle, then
RDYRTN takes precedence, causing the
next transfer cycle to begin with a T1 cycle.
BRDY functions as an output during PCnet-32 controller
slave cycles and is always driven inactive (HIGH).
BRDY is floated if the PCnet-32 controller is not being
accessed as the current slave device on the local bus.
D/C
Data/Control Select
Input/Output
During slave accesses to the PCnet-32 controller, the
D/
C pin, along with M/IO and W/R, indicates the type of
cycle that is being performed. PCnet-32 controller will
only respond to local bus accesses in which D/
C is
driven HIGH by the local bus master.
During PCnet-32 controller bus master accesses, the
D/
C pin is an output and will always be driven HIGH.
D/
C is floated if the PCnet-32 controller is not the current
master on the local bus.
DAT0–DAT31
Data Bus
Input/Output
Used to transfer data to and from the PCnet-32 control-
ler to system resources via the local bus. DAT31–DAT0
are driven by the PCnet-32 controller when performing
bus master writes and slave read operations. Data on
DAT31–DAT0 is latched by the PCnet-32 controller
when performing bus master reads and slave write
operations.
The PCnet-32 controller will always follow Am386DX
byte lane conventions. This means that for word and
byte accesses in which PCnet-32 controller drives the
data bus (i.e. master write operations and slave read
operations), the PCnet-32 controller will produce dupli-
cates of the active bytes on the unused half of the 32-bit
data bus. Table 6 illustrates the cases in which duplicate
bytes are created.
Table 6. Byte Duplication on Data Bus
BE3–
DAT
BE0
[31:24]
[23:16]
[15:8]
[7:0]
1110
Undef
A
1101
Undef
A
Undef
1011
Undef
A
Undef
Copy A
0111
A
Undef
Copy A
Undef
1100
Undef
B
A
1001
Undef
C
B
Undef
0011*
D
C
Copy D
Copy C
1000
Undef
C
B
A
0001
D
C
B
Undef
0000
D
C
B
A
*Note: Byte duplication does not apply during a
LBS16
access. See Table 8.
INTR1–INTR4
Interrupt Request
Output
An attention signal which indicates that one or more of
the following status flags is set: BABL, MISS, MERR,
RINT, IDON, MFCO, RCVCCO, TXSTRT, or JAB. Each
of these status flags has a mask bit which allows for
suppression of INTR assertion. These flags have the
meaning shown in Table 7.
Table 7. Status Flags
BABL
Babble (CSR0, bit 14)
MISS
Missed Frame (CSR0, bit 12)
MERR
Memory Error (CSR0, bit 11)
RINT
Receive Interrupt (CSR0, bit 10)
IDON
Initialization Done (CSR0, bit 8)
MFCO
Missed Packet Count Overflow
(CSR4, bit 9)
RCVCCO
Receive Collision Count Overflow
(CSR4, bit 5)
TXSTRT
Transmit Start (CSR4, bit 3)
JAB
Jabber (CSR4, bit 1)
Note that there are four possible interrupt pins, depend-
ing upon the mode that has been selected with the
JTAGSEL pin. Only one interrupt pin may be used at
one time. The active interrupt pin is selected by pro-
gramming the interrupt select register (BCR21). The
default setting of BCR121will select interrupt INTR1 as
the active interrupt. Note that BCR21 is EEPROM-pro-
grammable. Inactive interrupt pins are floated.
The polarity of the interrupt signal is determined by the
INTLEVEL bit of BCR2. The interrupt pins may be
programmed for level-sensitive or edge-sensitive
operation.
PCnet-32 controller interrupt pins will be floated at
H_RESET and will remain floated until either the
EEPROM has been successfully read, or, following an
EEPROM read failure, a Software Relocatable Mode
sequence has been successfully executed.
LBS16
Local Bus Size 16
Input
BS16 is sampled during PCnet-32 controller bus mas-
tering activity to determine if the target device on the
VL-Bus is 32 or 16 bits in width. If the
LBS16 signal is
sampled active at least one clock period before the as-
sertion of
LRDY during a PCnet-32 controller bus mas-
ter transfer, then the PCnet-32 controller will convert a
single 32-bit transfer into two 16-bit transfers. Not all
32-bit transfers need to be split into two 16-bit transfers.
Table 8 shows the sequence of transfers that will be
executed for each possible 32-bit bus transfer that en-
counters a proper assertion of the
LBS16 signal.