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CHAPTER 2 PIN FUNCTIONS
30
2.3.2 Bus Interface Signals
The
μ
PD98405 supports a PCI or general-purpose bus interface. PCI or general-purpose mode is selected
using the PCI_MODE signal.
The PCI bus interface can be connected directly to the PCI bus. The general-purpose bus interface can be
connected to a general I/O bus with a minimum of external circuitry.
(1) General-purpose bus interface signals (Level of the PCI_MODE pin: Low)
(1/4)
Symbol
Pin No.
I/O
I/O level
Function
AD31-AD0
3, 6, 9 - 12,
15 - 17,
34 - 36,
39 - 42, 45,
47, 48,
51 - 54,
57, 58,
295 - 297,
300 - 303
4
18
33
46
I/O
3-state
TTL
Address/Data
The AD31 to AD0 bus is a 32-bit, bi-directional, multiplexed
address/data bus. During the first clock of a transaction,
AD31 to AD0 contains a physical byte address. During
subsequent clocks, AD31 to AD0 contains data. When the
μ
PD98405 is not accessing the bus, it places the AD bus in
the high impedance state.
BE3_B
BE2_B
BE1_B
BE0_B
O
3-state
TTL
Byte Enable
The BE3_B to BE0_B signals determine whether their
corresponding bytes are valid in the
μ
PD98405 master cycle.
BE3_B corresponds to AD31 to AD24; BE0_B to AD7 to
AD0. When the
μ
PD98405 is not accessing the bus or
accessing the bus as the slave, the BE3_B to BE0_B signals
are placed in the high impedance state.
Bus Parity
The PAR indicates the parity across AD31 to AD0. Parity
checking is configured by setting the appropriate bits in the
GMR. Parity checking may be enabled/disabled, even/odd,
byte or word. When configured as byte parity, PAR3
represents AD31 to AD24 while PAR0 represents AD7 to
AD0. When configured as word parity, PAR2 to PAR0 have
no functions while PAR3 is a bi-directional signal: an output
during address and write data phases and input during read
data phases.
When the
μ
PD98405 is not accessing the bus it places
PAR3 to PAR0 in the high impedance state. Connect a pull-
up resistor when unused.
Output Enable
When the OE_B signal is low, the
μ
PD98405 controls AD31
to AD0 and PAR3 to PAR0 as 3-state bidirectional pins
(normal operation). When the OE_B signal is high, these
pins are placed in the high impedance state. This signal is
optional. Fix it to low unless the above pins need be forcibly
set to high impedance.
PAR3
PAR2
PAR1
PAR0
66
69
70
71
I/O
3-state
TTL
OE_B
59
I
TTL