6.2
Bulk IN Transfers
1
2
3
4
5
H
H
D
H
D
D
A
T
A
1
C
R
C
1
A
D
D
R
E
N
D
P
C
R
C
5
A
D
D
R
E
N
D
P
C
R
C
5
..
.
A
C
K
N
A
K
I
N
Payload
Data
I
N
...
6
Token Packet
Data Packet
Token Packet
H/S Pkt
H/S Pkt
(INnBC loaded)
EPnIN Interrupt, INnBSY=0
4
5
6
7
8
H
D
H
D
H
D
A
T
A
0
C
R
C
1
A
D
D
R
E
C
R
C
5
A
D
D
R
E
N
D
P
C
R
C
5
N
A
K
A
C
K
I
N
N
D
P
Payload
Data
I
N
...
...
6
Token Packet
Data Packet
Token Packet
H/S Pkt
H/S Pkt
Load INnBC
EPnIN Interrupt, INnBSY=0
Figure 6-3. Anatomy of a Bulk IN Transfer
USB bulk IN data travels from device to host. The host requests an IN transfer by issuing
an IN token to the EZ-USB core, which responds with data when it is ready. The 8051
indicates ready by loading the endpoint’s byte count register. If the EZ-USB core receives
an IN token for an endpoint that is not ready, it responds to the IN token with a NAK hand-
shake.
In the bulk IN transfer illustrated in Figure 6-3, the 8051 has previously loaded an end-
point buffer with a data packet, and then loaded the endpoint’s byte count register with the
number of bytes in the packet to arm the next IN transfer. This sets the endpoint’s BUSY
Bit. The host issues an IN token (1), to which the USB core responds by transmitting the
data in the IN endpoint buffer (2). When the host issues an ACK (3), indicating that the
data has been received error-free, the USB core clears the endpoint’s BUSY Bit and sets
its interrupt request bit. This notifies the 8051 that the endpoint buffer is empty. If this is a
multi-packet transfer, the host then issues another IN token to get the next packet.
If the second IN token (4) arrives before the 8051 has had time to fill the endpoint buffer,
the EZ USB core issues a NAK handshake, indicating busy (5). The host continues to send
Page 6-4
Chapter 6. EZ-USB CPU
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
