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CHAPTER 4 BUS CONTROL FUNCTION
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Normal status
Bus hold status
Normal status
4.7 Bus Hold Function
4.7.1 Outline of function
When P95 and P96 of port 9 are programmed to be in the control mode, the functions of the HLDRQ and HLDAK
pins become valid.
When the HLDRQ pin becomes active (low) indicating that another bus master is requesting acquisition of the bus,
the external address/data bus and strobe pins go into a high-impedance state, and the bus is released (bus hold
status). When the HLDRQ pin becomes inactive (high) indicating that the request for the bus is cleared, these pins
are driven again.
During bus hold period, the V853 continues internal operation until external memory access.
In the bus hold status, the HLDAK pin becomes active (low).
This feature can be used to design a system where two or more bus masters exist, such as when multi-processor
configuration is used and when a DMA controller is connected.
Bus hold request is not acknowledged between the first and the second access in word access. Bus hold request
is not acknowledged between read access and write access in read modify write access of bit manipulation instruction.
4.7.2 Bus hold procedure
The procedure of the bus hold function is illustrated below.
<1> HLDRQ = 0 accepted
<2> All bus cycle start request pending
<3> End of current bus cycle
<4> Bus idle status
<5> HLDAK = 0
<6> HLDRQ = 1 accepted
<7> HLDAK = 1
<8> Clears bus cycle start request pending
<9> Start of bus cycle
4.7.3 Operation in power save mode
In the STOP or IDLE mode, the system clock is stopped. Consequently, the bus hold status is not set even if the
HLDRQ pin becomes active.
In the HALT mode, the HLDAK pin immediately becomes active when the HLDRQ pin becomes active, and the
bus hold status is set. When the HLDRQ pin becomes inactive, the HLDAK pin becomes inactive. As a result, the
bus hold status is cleared, and the HALT mode is set again.
HLDRQ
HLDAK
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