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7.1.3
Pin Configuration
Table 7.1 lists the bus state controller pin configuration.
Table 7.1
Pin Configuration
Signal
I/O
With Bus
Released
Description
A26–A0
I/O
I
Address bus. 27 bits are available to specify a total 128 Mbytes of
memory space. The most significant 2 bits are used to specify the
CS space, so the size of the spaces is 32 Mbytes. When the bus is
released, these become inputs for the external bus cycle address
monitor.
D31–D0
I/O
Hi-Z
32-bit data bus. When reading or writing a 16-bit width area, use
D15–D0; when reading or writing a 8-bit width area, use D7–D0.
With 8-bit accesses that read or write a 32-bit width area, input and
output the data via the byte position determined by the lower
address bits of the 32-bit bus.
BS
I/O
I
Indicates start of bus cycle or monitor. With the basic interface
(device interfaces except for DRAM, synchronous DRAM, pseudo-
SRAM), signal is asserted for a single clock cycle simultaneous
with address output. The start of the bus cycle can be determined
by this signal. This signal is asserted for 1 cycle synchronous with
column address output in DRAM, synchronous DRAM and pseudo-
SRAM accesses. When the bus is released,
BS
becomes an input
for address monitoring of external bus cycles.
CS0
–
CS3
RD/
WR
,
WE
O
Hi-Z
Chip select. Signals that select area; specified by A26 and A25.
I/O
I
Read/write signal. Signal that indicates access cycle direction
(read/write). Connected to
WE
pin when DRAM/synchronous
DRAM is connected. When the bus is released, becomes an input
for address monitoring of external bus cycles.
RAS
pin for DRAM/synchronous DRAM.
CE
pin for pseudo-SRAM.
Open when using DRAM.
CAS
pin for synchronous DRAM.
OE
pin
for pseudo-SRAM.
When DRAM is used, connected to
CAS
pin for the most
significant byte (D31–D24). When synchronous DRAM is used,
connected to DQM pin for the most significant byte. When pseudo-
SRAM is used, connected to
WE
pin for the most significant byte.
For basic interface, indicates writing to the most significant byte.
When DRAM is used, connected to
CAS
pin for the second byte
(D23–D16). When synchronous DRAM is used, connected to DQM
pin for the second byte. When pseudo-SRAM is used, connected
to
WE
pin for the second byte. For basic interface, indicates writing
to the second byte.
RAS
,
CE
CAS
,
OE
O
Hi-Z
O
Hi-Z
CASHH
,
DQMUU,
WE3
O
Hi-Z
CASHL
,
DQMUL,
WE2
O
Hi-Z