h8s-2158 Renesas Electronics Corporation., h8s-2158 Datasheet - Page 242

• Manufacturer Part Number: h8s-2158
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

Section 8 RAM-FIFO Unit (RFU)
The total of the above cycles is 5 to 13 states. Cycles for synchronization of the peripheral module
clock with the system clock are needed even when the hardware FIFO is used instead of the RFU.
Therefore, RAM-FIFO overhead by the RFU is 3 to 10 states (except for wait states for external
extension). To reduce the RFU response time, it is recommended to set the external extension area
access to 3 states/no waits.
Rev. 3.00 Jan 25, 2006 page 190 of 872
REJ09B0286-0300
RFU bus cycle: 2 states
Cycle to synchronize the RFU signal with the peripheral module clock: 1 and 2 states
(depending on the peripheral module clock)
12-MHz clock
for the USB
SB0V *
SB1V *
RFU activation
request
RFU bus cycle
Notes: 1. USB SENDBUFCR SB0V bit: Transmit buffer 0 valid bit
1
2
2. USB SENDBUFCR SB1V bit: Transmit buffer 1 valid bit
CPU bus cycle
T1
synchronization cycle
T2
System clock
Figure 8.3 Example of RFU Response Time
CPU bus cycle
T1
Request output
T2
cycle
CPU bus cycle
T1
for the end of
Cycle to wait
the current
bus cycle
T2
RFU bus cycle
RFU bus cycle
T1
T2
Synchronization
the peripheral
module clock
cycle with
CPU bus cycle
T1
T2
synchronizatioin
System clock
cycle
CPU bus cycle
T1
T2