Fujitsu FR81S ユーザーズマニュアル
CHAPTER 36: EXTERNAL BUS INTERFACE
5. Operation
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : EXTERNAL BUS INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
26
Operating example description
cycle1 :
"L" is output to ASX to indicate that access is starting from this cycle. Address information A0 is
output to data bus D16 to D31. ASX functions as the strobe signal for this address information. This address
information is output for the configured count cycles. After the configured count has finished, D16 to D31
are put into the input state.
cycle2 :
After the configured count has finished from the access starting, "L" is output to CSnX (n= 0 to 3)
continually until the access is complete. Devices on the external bus need to perform processing for the
access only within the period where CSnX="L".
cycle3 :
"L" is output to RDX after the configured count from when CSnX="L" output is started. External
bus devices are required to return read data to D16 to D31 within the strobe period indicated by RDX="L".
cycle4
: The output to RDX returns to "H" after the configured count finishes after output of RDX="L"
begins. The data on D16 to D31 is fetched into the internal buffer on the rising edge of the final SYSCLK
within the period where RDX="L".
cycle5 :
The output of CSnX (n=0 to 3) returns to "H" after the configured count finishes from when RDX
returns to "H", and the read access finishes. In this example, CSnX returns to "H" when this cycle ends and
the read access finishes.
Signal description
External bus output signals are synchronized to the rising edge of SYSCLK.
ASX
Indicates the start of access. This also functions as the address strobe.
An "L" pulse is output for a period of 1 or 2 cycles from when the access starts.
CSnX (n=0 to 3)
Indicates that the access destination address is within the corresponding CS area. External bus devices are
required to process requests from the bus only when this signal is "L". After the configured count has
finished from when the access started, "L" begins to be output, and this continues until the access finishes.
RDX
Indicates the period of the read strobe. After the configured count ends from when CSnX (n=0 to 3) is
driven, this outputs "L" for read access. This returns to output "H" after the read auto wait count has ended.
The external bus device is required to return valid data in D16 to D31 within the period where RDX="L".
This module fetches the D16 to D31 data into the internal buffer on the rising edge of the final SYSCLK
within the period where RDX="L".
D16 to D31
Address information is output from when the access begins. After the configured count has finished, this
enters the input state and accepts the read data from the external bus device. This module fetches the D16 to
D31 data into the internal buffer on the rising edge of the final SYSCLK within the period where
RDX="L".
MB91520 Series
MN705-00010-1v0-E
1225