CHAPTER 4 BUS CONTROL FUNCTION
User’s Manual U13850EJ4V0UM
113
4.7 Bus Hold Function
4.7.1 Outline of function
When the MM3 bit of the memory expansion mode 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.
The bus hold status can be recognized by that 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, and not acknowledged
between read access and write access in read modify write access of bit manipulation instruction either.
Note
A1 to A15 are retained when a separate bus is used.
Содержание MPD703030A
Страница 2: ...User s Manual U13850EJ4V0UM 2 MEMO ...
Страница 514: ...User s Manual U13850EJ4V0UM 514 MEMO ...