HD6412350 Hitachi, HD6412350 Datasheet - Page 208

• Manufacturer Part Number: HD6412350
• Description: (HD6412350 / HD6432351) 16-BIT MICROCONTROLLER
• Manufacturer: Hitachi

6.10.5
When MSTPCR is set to H'FFFF or H'EFFF and a transition is made to sleep mode, the external
bus release function halts. Therefore, MSTPCR should not be set to H'FFFF or H'EFFF if the
external bus release function is to be used in sleep mode.
6.11
6.11.1
The H8S/2350 Series has a bus arbiter that arbitrates bus master operations.
There are three bus masters, the CPU, DTC, and DMAC, which perform read/write operations
when they have possession of the bus. Each bus master requests the bus by means of a bus request
signal. The bus arbiter determines priorities at the prescribed timing, and permits use of the bus by
means of a bus request acknowledge signal. The selected bus master then takes possession of the
bus and begins its operation.
6.11.2
The bus arbiter detects the bus masters' bus request signals, and if the bus is requested, sends a bus
request acknowledge signal to the bus master making the request. 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:
An internal bus access by an internal bus master, external bus release, and refreshing, can be
executed in parallel.
In the event of simultaneous external bus release request, refresh request, and internal bus master
external access request generation, the order of priority is as follows:
As a refresh and an external access by an internal bus master can be executed simultaneously,
there is no relative order of priority for these two operations.
188
Usage Note
Bus Arbitration
Overview
Operation
(High)
(High) Refresh > External bus release (Low)
(High) External bus release > Internal bus master external access (Low)
DMAC
>
DTC
>
CPU
(Low)