38K2 datasheet(89/358 Pages) RENESAS

89 / 358 page

FUNCTIONAL DESCRIPTION

Rev.2.00

Oct 15, 2006

page 70 of 130

38K2 Group

REJ09B0338-0200

HARDWARE

EXTERNAL BUS INTERFACE (EXB)

The external bus interface (EXB) controls the data transfer be-

tween the external MCU and the 38K2 group’s CPU or its

qCPU channel

It is a data transfer course by the interrupt processing between the

external MCU and the 38K2 group’s CPU.

qMemory channel

It is a data transfer course by direct RAM access of the memory

channel controller between the external MCU and the 38K2

group’s memory (multichannel RAM)

CPU channel

[Interrupt type]

Memory channel

[Direct RAM access type]

38K2 group

USB bus

(USB host)

CPU

Program ROM

Peripheral functions

External bus interface

(EXB)

USB

Multichannel RAM

Fig. 103 External bus interface

Address

CS, RD, WR,

DMA acknowledge

Access cycle time from externals:

•3 clocks or more of

φ + Signal delay time + Data setup

time of external MCU in USB inactive

•5 clocks or more of

φ + Signal delay time + Data setup

time of external MCU in USB active

Fig. 104 Data transfer timing of memory channel

memory (multichannel RAM). The external bus interface is shown

below.

qData transfer of memory channel

When the burst mode is selected with the burst bit of the memory

channel operation mode register, data transfer can be carried out

at the highest speed. After the external bus interface detects a rise

of external read signal/write signal and synchronizes it with the in-

ternal clock

φ, it completes the data transfer between the transmit/

receive buffer and the multichannel RAM in two clocks.

However, the waiting time of two clocks at a maximum is gener-

ated to access the multichannel RAM in USB being operating

because the USB has priority to access.

Therefore, it is necessary to set up the access interval which fills

the following timing with the external MCU bus side.

φ = 8 MHz, data transfer at about 2 Mbytes/second is possible

at a maximum. When there is access simultaneously from the

USB, it is about 1.3 Mbytes/second.

φ = 6 MHz, data transfer at about 1.5 Mbytes/second is possible

at a maximum. When there is access simultaneously from the

USB, it is about 1 Mbytes/second.

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