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Chapter 4
Bus Control Function
Preliminary User’s Manual U15839EE1V0UM00
4.11 Boundary Operation Conditions
4.11.1 Program
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(1)
Branching to the peripheral I/O area or successive fetch from the internal RAM area to the internal
peripheral I/O area is inhibited. In terms of hardware, fetching the NOP opcode continues, and
fetching from the external memory is not performed.
(2)
If a branch instruction exists at the upper limit of the internal RAM area, a pre-fetch operation
(invalid fetch) that straddles over the internal peripheral I/O area does not occur when instruction
fetch is performed.
4.11.2 Data
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The V850E/CA2 Jupiter is provided with an address misalign function.
Through this function, regardless of the data format (word data, halfword data, or byte data), data can
be placed in all addresses. However, in the case of word data and halfword data, if data are not sub-
jected to boundary alignment, the bus cycle will be generated a minimum of 2 times and bus efficiency
will drop.
(1)
In the case of halfword length data access
When the address's LSB bit is 1, the byte length bus cycle will be generated 2 times.
(2)
In the case of word length data access
(a) When the address's LSB is 1, bus cycles will be generated in the order of byte length bus
cycle, halfword length bus cycle, and word length bus cycle.
(b) When the address's lowest 2 bits are 10, the halfword length bus cycle will be generated 2
times.
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