HD64F2145 datasheet(174/829 Pages) RENESAS

174 / 829 page

Rev. 2.0, 08/02, page 134 of 788

6.8

Bus Arbitration

The bus controller has a bus arbiter that arbitrates bus master operations. There are two bus

masters – the CPU and DTC – that perform read/write operations when they have possession of

the bus.

6.8.1

Priority of Bus Masters

Each bus master requests the bus by means of a bus request signal. The bus arbiter detects the bus

masters' bus request signals, and if a bus request occurs, it sends a bus request acknowledge signal

to the bus master making the request at the designated timing. If there are bus requests from more

than one bus master, the bus request acknowledge signal is sent to the one with the highest

priority. When a bus master receives the bus request acknowledge signal, it takes possession of the

bus until that signal is canceled. The order of priority of the bus masters is as follows:

(High) DTC > CPU (Low)

6.8.2

Bus Transfer Timing

When a bus request is received from a bus master with a higher priority than that of the bus master

that has acquired the bus and is currently operating, the bus is not necessarily transferred

immediately. Each bus master can relinquish the bus at the timings given below.

CPU: The CPU is the lowest-priority bus master, and if a bus request is received from the DTC,

the bus arbiter transfers the bus to the DTC.

• DTC bus transfer timing

 The bus is transferred at a break between bus cycles. However, if a bus cycle is executed in

discrete operations, as in the case of a longword-size access, the bus is not transferred

between the component operations. For details, refer to the H8S/2600 Series, H8S/2000

Series Programming Manual.

 If the CPU is in sleep mode, the bus is transferred immediately.

DTC: The DTC has the highest bus master priority. The DTC sends the bus arbiter a request for

the bus when an activation request is generated. The DTC does not release the bus until it

completes its operation.

HD64F2145 Datasheet(PDF) 174 Page - Renesas Technology Corp