MCF548x Reference Manual, Rev. 3
29-36 Freescale Semiconductor

If a register write occurs at the same time an interrupt is received, the interrupt takes precedence over the

write.

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
R00000000000000 0 0
W
Reset Uninitialized
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
R0000000FUEMTERRFIFO
HI
FIFO
LO
0EOT 0 EOF
W
Reset Uninitialized 0 1 0 0 0 Unin. 0 Unin. 0
Reg
Addr
MBAR + 0xB444 (EP0ISR); 0xB474 (EP1ISR); 0xB4A4 (EP2ISR); 0xB4D4 (EP3ISR);
0xB504 (EP4ISR); 0xB534 (EP5ISR); 0xB564 (EP6ISR)

Figure 29-42. USB Endpoint n Interrupt Status Register (EPnISR)

Table 29-37. EPnISR Field Descriptions

Bits Name Description
31–9 — Reserved, should be cleared.
8 FU FIFO full. This is the FIFO full indicator. For OUT endpoints, this interrupt may assert in cases where
OUT packet data fills the FIFO and is subsequently discarded due to an incorrect CRC calculation.
Because of this, the FU bit in the FIFO status register (EPnFSR) should be checked to verify that
the OUT endpoint FIFO is actually full.
0 Indicates that the FIFO is not full.
1 Indicates that the FIFO is full.
7 EMT FIFO empty. This is the FIFO empty indicator. For OUT endpoints, this interrupt may assert in cases
where OUT packet data is written to an empty FIFO and is subsequently discarded due to an
incorrect CRC calculation. Because of this, the EMT bit in the FIFO status register (EPnFSR) should
be checked to verify that the OUT endpoint FIFO is actually empty.
For IN endpoints, this interrupt may assert in cases where only one packet of data is stored in the
FIFO and that packet must be retried because it encounters an error while being sent to the host.
In this scenario, the FIFO will be temporarily empty before the retry operation causes the read
pointer to rewind. Thus, the EMT interrupt will set because of the temporary empty state of the FIFO.
Because of this, the EMT bit in the FIFO status register (EPnFSR) should be checked to verify that
the IN endpoint FIFO is actually empty.
0 Indicates that the FIFO is not empty.
1 Indicates that the FIFO is empty.
6 ERR FIFO error. This indicates an error condition in the FIFO controller. The error condition can be
checked by reading the FIFO status register (EPnFSR).
0 No Error condition pending.
1 Error condition pending.
5 FIFOHI FIFO high. This indicates that the number of bytes in the FIFO has surpassed the high level alarm
value.
4 FIFOLO FIFO low. This indicates that the number of bytes in the FIFO has fallen below the FIFO low level
alarm value.