CHAPTER 5 BUS CONTROL FUNCTION
User’s Manual U15905EJ2V1UD
193
5.8
Bus Hold Function
5.8.1
Functional outline
The HLDAK and HLDRQ functions are valid if the PCM2 and PCM3 pins are set in the control mode.
When the HLDRQ pin is asserted (low level), indicating that another bus master has requested bus mastership, the
external address/data bus goes into a high-impedance state and is released (bus hold status). If the request for the
bus mastership is cleared and the HLDRQ pin is deasserted (high level), driving these pins is started again.
During the bus hold period, execution of the program in the internal ROM and internal RAM is continued until a
peripheral I/O register or the external memory is accessed.
The bus hold status is indicated by assertion of the HLDAK pin (low level). The bus hold function enables the
configuration multi-processor type systems in which two or more bus masters exist.
Note that the bus hold request is not acknowledged during a multiple-access cycle initiated by the bus sizing
function or a bit manipulation instruction.
Status
Data Bus
Width
Access Type
Timing in Which Bus Hold Request
Not Acknowledged
Word access to even address
Between first and second access
Word access to odd address
Between second and third access
16 bits
Halfword access to odd address
Between first and second access
Between second and third access
Word access
Between third and fourth access
CPU bus lock
8 bits
Halfword access
Between first and second access
Read-modify-write access of bit
manipulation instruction
Between read access and write
access
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