Datasheet

Table Of Contents
Section 15 Universal Serial Bus Interface (USB)
Page 596 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
15.9.10 Level Shifter for VBUS and IRQx Pins
The VBUS and IRQx pins of this USB module must be connected to the USB connector’s VBUS
pin via a level shifter. This is because the USB module has a circuit that operates by detecting
USB cable connection or disconnection.
Even if the power of the device incorporating this USB module is turned off, 5-V power is applied
to the USB connector’s VBUS pin while the USB cable is connected to the device set. To protect
the LSI from destruction, use a level shifter such as the HD74LV-A series, which allows voltage
application to the pin even when the power is off.
15.9.11 Read and Write to USB Endpoint Data Register
To write data to an USB endpoint data register (UEDRni) on the transmit side using a CPU word
or longword transfer instruction, the correct size of data must be written to the USB endpoint data
register. Otherwise, an error may occur.
For example, when 7-byte data is transferred to the host, 8-byte data is sent to the host if data is
written twice by the longword transfer instructions or if data is written four times by the word
transfer instructions. To write 7-byte data correctly, data must be written once by a longword
transfer instruction, once by a word transfer instruction, and once by a byte transfer instruction, or
data must be written three times by a word transfer instruction and once by a byte transfer
instruction.
To read data from the USB endpoint data register (UEDRno) on the receive side, the correct size
of data must be read. In this case, the data size is specified by the USB endpoint receive size data
register (UESZno).
To execute DMA transfer on data in the USB endpoint data register using the on-chip DMAC,
byte transfer musts be used. In word transfer, odd-byte data cannot be transferred. Word transfer is
thus disabled.
15.9.12 Restrictions for Software Standby Mode Transition
Before entering the software standby mode, disabled the SOF marker function and set the USB
module stop state as shown in figure 15.34. The UDC core must not be reset.
To access the USB module after software standby mode, cancel the USB module stop state and
wait for the USB operating clock (48 MHz) stabilization time as shown in figure 15.34.