Datasheet

Section 14 Universal Serial Bus (USB)
Rev.7.00 Dec. 24, 2008 Page 482 of 698
REJ09B0074-0700
14.3.17 USB Interrupt Flag Register 1 (UIFR1)
UIFR1 is an interrupt flag register indicating the EP1 and EP2 status. If the corresponding bit is set
to 1, the corresponding EXIRQ0 or EXIRQ1 interrupt is requested to the CPU. EP1TR flags can
be cleared by writing 0 to them. Writing 1 to them is invalid and causes no operation.
Consequently, to clear a flag, write 0 to the corresponding bit and 1 to all the other bits. (For
example, write H'FD to clear bit 1.) The bit-clear instruction is a read/modify/write instruction, so
if a new flag is set between the read and write operations, there is a danger that it may be cleared
erroneously. Therefore, do not use the bit-clear instruction to clear bits in this interrupt flag
resister. However, EP1EMPTY, EP2READY, and EP1ALLEMPTYs are status bits to indicate the
EP1, EP2, and FIFO state respectively, and cannot be cleared.
Bit Bit Name Initial Value R/W Description
7 to 4 — All 0 R Reserved
These bits are always read as 0 and cannot be
modified.
3 EP1ALL
EMPTYs
1 R EP1 FIFO All Empty Status
EP1 FIFO has a dual-FIFO configuration. This bit is set
to 1 if there is no valid data in both FIFOs. This
corresponds to the negative-electrode signal for the
EP1DE bit in UDSR.
An interrupt cannot be required by EP1ALLEMPTY.
2 EP2READY 0 R EP2 Data Ready
EP2 FIFO has a dual-FIFO configuration. This bit is set
to 1 if there is valid data at least in either of FIFOs.
This bit is cleared to 0 if there is no valid data in both
FIFOs. This bit is a status bit and cannot be cleared.
The corresponding interrupt output is EXIRQ0 or
EXIRQ1.
1 EP1TR 0 R/(W)* EP1 Transfer Request
Set to 1 if there is no valid data in both FIFOs when an
IN token is sent from the host to EP1. The
corresponding interrupt output is EXIRQ0 or EXIRQ1.
0 EP1EMPTY 1 R EP1 FIFO Empty
EP1 FIFO has a dual-FIFO configuration. This bit is set
to 1 if there is no valid data at least in either of FIFOs.
This bit is cleared to 0 if there is valid data in both
FIFOs. This bit is a status bit and cannot be cleared.
The corresponding interrupt output is EXIRQ0 or
EXIRQ1.
Note:* The write value should always be 0 to clear this flag.