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248
Rabbit 4000 Microprocessor User’s Manual
24.1.2 I/O Strobes
There are eight I/O strobes available in the Rabbit 4000. Each has a separate 8KB address
range that can be enabled as a chip select, read strobe, write strobe, or a read/write strobe.
The number of wait states can be set to 1, 3, 7, or 15, and the signal can be active high or
low.
The I/O strobes can be used for devices on the memory bus or the auxiliary I/O bus, and
can be enabled to go out on the memory bus alone or both buses. It is also possible to
shorten the read strobe by one clock cycle and the write strobe by one-half a clock cycle
by pulling in the trailing edge, which guarantees one clock cycle of hold time for transac-
tions.
Figure 24-1. Auxiliary I/O Bus Cycles
Table 24-1. External I/O Strobes
Register
External I/O Address Range
IB0CR
0x0000–0x1FFF
IB1CR
0x2000–0x3FFF
IB2CR
0x4000–0x5FFF
IB3CR
0x6000–0x7FFF
IB4CR
0x8000–0x9FFF
IB5CR
0xA000–0xBFFF
IB6CR
0xC000–0xDFFF
IB7CR
0xE000–0xFFFF
ADDR
WRITE DATA
READ DATA
WRITE STROBE
CHIP SELECT STROBE
READ STROBE
EXTERNAL I/O TIMING (with 1 wait state)
T1
Tw
T2
valid
valid
valid
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