CHAPTER 4 BUS CONTROL FUNCTION
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4.7 Bus Hold Function
4.7.1 Outline of function
MM3 bit of the memory expansion register (MM) is set (1), the HLDRQ and HLDAK pin functions of P95 and P96
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
Note
, 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 internal operation continues until the next 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 word access. Bus hold request is also not
acknowledged between read access and write access in read modify write access of bit manipulation instruction.
Note A1 to A15 pins are retained when the separate bus is used.
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