Datasheet

Table Of Contents
Section 15 Universal Serial Bus Interface (USB)
Page 600 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
15.9.17 Notes on UIFRO
The bit-clear instruction cannot be used to clear a flag in some USB interrupt flag registers to 0.
These registers have flags which are cleared to 0 by writing 0 and to which writing 1 is ignored.
The concerning registers are USB interrupt flag registers 0 to 3 (UIFR0 to UIFR3) in the
H8S/2215 Group.
A single bit-clear instruction actually executes reading the value of a register, modifying the read
value, and writing the modified value. When clearing a flag with the bit-clear instruction, if a
source which will set another flag is activated between reading and writing, the flag is
unintentionally cleared to 0. Therefore, the bit-clear instruction cannot be used.
To clear these flags, write 0 to a flag which should be cleared and write 1 to other flags with the
MOVE instruction. For example, to clear only bit 7, write H'7F and to clear bits 6 and 7, write
H'3F.
15.9.18 Clearing the FIFOs in DMA Transfer Mode
When DMA transfers are enabled at endpoints 2 and 4, it is not possible to clear the EP2o
OUTFIFO and EP4o OUTFIFO. To clear the FIFOs, first disable DMA transfers.