
EZ-USB FX2 Technical Reference Manual
Page 4-14 EZ-USB FX2 Technical Reference Manual v2.1
4.4.2.7 Endpoint Interrupts
These interrupts are asserted when an endpoint requires service.
For an OUT endpoint, the interrupt request signifies that OUT data has been sent from the host,
validated by the FX2, and is in the endpoint buffer memory.
For an IN endpoint, the interrupt request signifies that the data previously loaded by the FX2 into
the IN endpoint buffer has been read and validated by the host, making the IN endpoint buffer
ready to accept new data.
4.4.2.8 In-Bulk-NAK (IBN) Interrupt
When the host sends an IN token to any IN endpoint which does not have data to send, the FX2
automatically NAKs the IN token and asserts this interrupt.
4.4.2.9 EPxPING Interrupt
These interrupts are active only during high speed (480 Mbits/sec) operation.
USB 2.0 improves the USB 1.1 bus bandwidth utilization by implementing a PING-NAK mecha-
nism for OUT transfers. When the host wishes to send OUT data to an endpoint, it first sends a
PING token to see if the endpoint is ready (i.e. if it has an empty buffer). If a buffer is not available,
the FX2 returns a NAK handshake. PING-NAK transactions continue to occur until an OUT buffer
is available, at which time the FX2 answers a PING with an ACK handshake and the host sends
the OUT data to the endpoint.
The EPxPING interrupt is asserted when the host PINGs an endpoint and the FX2 responds with
a NAK because no endpoint buffer memory is available.
Table 4-11. Endpoint Interrupts
EP0-IN EP0-IN ready to be loaded with data (BUSY bit 1-to-0)
EP0-OUT EP0-OUT has received USB data (BUSY bit 1-to-0)
EP1-IN EP1-IN ready to be loaded with data (BUSY bit 1-to-0)
EP1-OUT EP1-OUT has received USB data (BUSY bit 1-to-0)
EP2 IN: Buffer available (Empty Flag 1-to-0)
OUT: Buffer has received USB data (Empty Flag 0-to-1)
EP4 IN: Buffer available (Empty Flag 1-to-0)
OUT: Buffer has received USB data (Empty Flag 0-to-1)
EP6 IN: Buffer available (Empty Flag 1-to-0)
OUT: Buffer has received USB data (Empty Flag 0-to-1)
EP8 IN: Buffer available (Empty Flag 1-to-0)
OUT: Buffer has received USB data (Empty Flag 0-to-1)
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