DF2211NP24V Renesas Technology / Hitachi Semiconductor, DF2211NP24V Datasheet - Page 205

• Manufacturer Part Number: DF2211NP24V
• Description: H8S/2200 Series, 2212 Group, USB, RTC, HSS TNP-64B; Vcc= 2.7 to 3.6 volts, Temp= -20 to 75 C; Package: PVQN0064LB-A
• Manufacturer: Renesas Technology / Hitachi Semiconductor

Write after Read: If an external write occurs after an external read while the ICIS0 bit in BCRH
is set to 1, an idle cycle is inserted at the start of the write cycle.
Figure 6.23 shows an example of the operation in this case. In this example, bus cycle A is a read
cycle from ROM with a long output floating time, and bus cycle B is a CPU write cycle. In (a), an
idle cycle is not inserted, and a collision occurs in cycle B between the read data from ROM and
the CPU write data. In (b), an idle cycle is inserted, and a data collision is prevented.
Relationship between Chip Select (CS) Signal and Read (RD) Signal: Depending on the
system's load conditions, the RD signal may lag behind the CS signal. An example is shown in
figure 6.24.
In this case, with the setting for no idle cycle insertion (a), there may be a period of overlap
between the bus cycle A RD signal and the bus cycle B CS signal.
Setting idle cycle insertion, as in (b), however, will prevent any overlap between the RD and CS
signals.
In the initial state after reset release, idle cycle insertion (b) is set.
Address bus
CS (area A)
CS (area B)
Data bus
HWR
RD
φ
(a) Idle cycle not inserted
(ICIS0 = 0)
T
Bus cycle A
1
Figure 6.23 Example of Idle Cycle Operation (2)
Long output floating time
T
2
T
3
Bus cycle B
T
1
T
2
Data collision
Address bus
CS (area A)
CS (area B)
Data bus
HWR
RD
φ
Rev.7.00 Dec. 24, 2008 Page 151 of 698
T
1
Bus cycle A
(b) Idle cycle inserted
(Initial value ICIS0 = 1)
T
2
T
3
T
Bus cycle B
I
REJ09B0074-0700
T
1
T
2