
Rev. 1.0, 09/01, page 231 of 904
T
1
Internal address bus
A23 to A0
External write cycle
,
T
2
T
W
T
W
T
3
On-chip memory read
Internal I/O register read
Internal read signal
D15 to D0
External address
Internal memory
External space
write
Internal I/O register address
Figure 6.83 Example of Timing when Write Data Buffer Function is Used
6.11
Bus Release
This LSI can release the external bus in response to a bus request from an external device. In the
external bus released state, internal bus masters except the EXDMAC continue to operate as long
as there is no external access. If any of the following requests are issued in the external bus
released state, the
%5(42
signal can be driven low to output a bus request externally.
•
When an internal bus master wants to perform an external access
•
When a refresh request is generated
•
When a SLEEP instruction is executed to place the chip in software standby mode or all-
module-clocks-stopped mode
6.11.1
Operation
In externally expanded mode, the bus can be released to an external device by setting the BRLE
bit to 1 in BCR. Driving the
%5(4
pin low issues an external bus request to this LSI. When the
%5(4
pin is sampled, at the prescribed timing the
%$&.
pin is driven low, and the address bus,
data bus, and bus control signals are placed in the high-impedance state, establishing the external
bus released state.
Содержание H8S/2376 F-ZTAT
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