Fujitsu FR81S User Manual
CHAPTER 36: EXTERNAL BUS INTERFACE
4. Registers
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : EXTERNAL BUS INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
14
[bit17, bit16] WRCV[1:0] (Write ReCoVery cycle) : Write Recovery Cycle
WRCV[1:0] is the write recovery cycle setting and is configured to control access to devices that have a
limit on the interval between a write access and the next access. During write recovery cycles, all of the
chip select signals are negated and write strobe signals WRnX (n=0, 1) is also held negated. Furthermore,
new accesses are not started within this period. When the write recovery cycle is set to 1 cycle or higher, the
write recovery cycle is always inserted after the write access.
WRCV[1:0]
Write recovery cycle
00
0 cycle (AWR0 Initial value)
01
1 cycle
10
2 cycles
11
3 cycles
[bit15, bit14] CSRD[1:0] (CSnX to RDX setup cycle) : CSnX to RDX Setup Cycle
CSRD[1:0] configures the read access CSnX to RDX setup cycles which set the period until RDX is
asserted after CSnX is asserted.
In order to correctly establish the protocol when address/data multiplex bus is configured (ACR:BSTY=1),
set the AWR parameters to satisfy the following conditions.
ACS + CSRD
≥
1 and ACS + CSWR
≥
1
CSRD[1:0]
CSnX → RDX Setup extension cycle
00
0 cycle
01
1 cycle
10
2cycles
11
3 cycles (AWR0 Initial value)
[bit13, bit12] RDCS[1:0] (RDX to CSnX hold cycle) : RDX to CSnX Hold Cycle
RDCS[1:0] configures the read access RDX to CSnX hold cycles which set the period until CSnX is
negated after RDX is negated.
RDCS[1:0]
RDX → CSnX hold extension cycle
00
0 cycle
01
1 cycle
10
2 cycles
11
3 cycles (AWR0 Initial value)
MB91520 Series
MN705-00010-1v0-E
1213