Fujitsu FR81S User Manual
CHAPTER 36: EXTERNAL BUS INTERFACE
5. Operation
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : EXTERNAL BUS INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
22
5.2. External Bus Signal Protocol
This section shows the external bus signal protocol.
5.2.1. Address/Data Split Bus Read Protocol
This section shows the protocol for read access using an address/data split bus.
Figure 5-1 Address/data split bus (Read operation example)
Operating example description
cycle1 :
"L" is output to ASX for 1 cycle to indicate that access is starting from this cycle. A00 to A21
indicate the address information of the access destination for this cycle.
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. STU fetches data from D16 to D31 to the internal buffer at the rising edge for the last SYSCLK
within the period RDX=L.
cycle5 :
The output of CSnX 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.
A0
D0
cycle no.
SYSCLK
ASX
A00 to A21
CSnX
(n=0,1,2,3)
RDX
H:
Dxx is input
L:
D
x
x
7
0
6
5
4
3
2
1
Dxx is output
MB91520 Series
MN705-00010-1v0-E
1221