h8s-2158 Renesas Electronics Corporation., h8s-2158 Datasheet - Page 240

• 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)
8.7
8.7.1
As this LSI supports medium-speed mode, current consumption can be reduced by dividing the
operating clock of the bus master. On the other hand, high-speed response may be requested of the
RFU, which is one of the bus masters. In particular, if the RFU is used as a slave of a host
interface, such as the USB, transfer data should be supplied with a sufficient transfer rate.
The RFU does not support medium-speed mode. The clock division in the medium-speed mode
should be temporarily suspended to switch the clock to high-speed mode by setting the DTSPEED
bit in SBYCR to 1 during DTC and RFU operations (and during CPU operation when transfer
request is generated).
Rev. 3.00 Jan 25, 2006 page 188 of 872
REJ09B0286-0300
Bus master clock
RFU activation
request
Bus master clock
RFU activation
request
The clock division is restored to high-speed mode from medium-speed mode after high-speed 1- to 2-state clocks
when the RFU activation request is generated.
RFU Bus Cycle
Clock Division
Figure 8.2 Examples of Temporary Cancellation of Medium-Speed Mode
T1
T1
CPU bus cycle
CPU bus cycle
T2
T2
2 states
1 state
CPU bus cycle
CPU bus cycle
T1
T1
T2
T2
RFU bus cycle
RFU bus cycle
T1
T1
T2
T2
T1
T1
CPU bus cycle
CPU bus cycle
T2
T2