EZ-Link (AN2720SC)
AN2720 E
NDPOINTS
Figure below illustrates the AN2720 endpoints and how they are connected between two
computers A and B.
(A)
EP0
Control
endpoints
Status
Interrupt
(B)
EP0
(A)
EP1
(B)
EP1
(A)
EP2
OUT
Computer (A)
15 packet buffer
(15 X 64 bytes)
(B)
EP2
IN
Computer (B)
(A)
EP2
IN
15 packet buffer
(15 X 64 bytes)
(B)
EP2
OUT
(A)
EP3
OUT
1 packet buffer
(64 bytes)
(B)
EP3
IN
(A)
EP3
IN
1 packet buffer
(64 bytes)
(B)
EP3
OUT
AN2720 endpoints and FIFOS
Endpoint zero is the default CONTROL endpoints required by every USB device.
Endpoint 1 is an INTERRUPT endpoint, useful for communicating with the PC driver.
Endpoints 2 and 3 are used to transfer USB BULK data. Endpoint 2 has extensive buffering (15
packets of 64 bytes each) and is designed to transfer high-bandwidth data. Endpoint 3, with a
single packet of buffering, can be used as a higher priority channel for driver communication.
Endpoints 2 and 3 operate similarly to each other, differing only by the amount of buffering
between the computers. Considering endpoint 2, when Computer (A) sends a packet over its
endpoint 2 OUT, the packet is stored in the 15-packet FIFO. If Computer (B) does not send any
IN tokens to its endpoint 2 (to retrieve a packet) by the time fifteen packets have been stored, the
AN2720 NAKS the next OUT packet from Computer (A). This handshake is maintained by both
endpoints 2 and 3, in both directions. When one side is unplugged, all packets are flushed from
the FIFOS, and the AN2720 NAKS all IN and OUT tokens from the attached side.
AN2720 Data Sheet Version 1.0
06/07/00
Page 5
CYPRESS [ CYPRESS SEMICONDUCTOR ]
