Table 10-2. EZ-USB States After a USB Bus Reset
Default
Value
Item
Register
Endpt Data
Comment
1
2
3
4
5
6
7
8
9
uuuuuuuu u = unchanged
Byte Counts
CPUCS
uuuuuuuu
uuuuuuuu
PORT Configs
PORT Registers
PORT OEs
uuuuuuuu
uuuuuuuu
uuuuuuuu
Interrupt Enables
Interrupt Reqs
Bulk IN C/S
uuuuuuuu
uuuuuuuu
00000000 unarm
10 Bulk OUT C/S
11 Toggle Bits
12 USBCS
uuuuuuuu retain armed/unarmed state
00000000
uuuuuuuu ReNum bit unchanged
13 FNADDR
00000000 USB Function Address
14 IN07VAL
uuuuuuuu
uuuuuuuu
uuuuuuuu
uuuuuuuu
uuuuuuuu
0
15 OUT07VAL
16 INISOVAL
17 OUTISOVAL
18 USBPAIR
19 Configuration
20 Alternate Setting
0
A USB bus reset leaves most EZ-USB resources unchanged. From Table 10-2, after USB
bus reset:
•
The EZ-USB core unarms all Bulk IN endpoints (9). Data loaded by the 8051 into
an IN endpoint buffer remains there, and the 8051 firmware can either re-send it by
loading the endpoint byte count register to re-arm the transfer, or send new data by
re-loading the IN buffer before re-arming the endpoint.
•
Bulk OUT endpoints retain their busy states (10). Data sent by the host to an OUT
endpoint buffer remains in the buffer, and the 8051 firmware can either read the
data or reject it as stale simply by not reading it. In either case, the 8051 loads a
dummy value to the endpoint byte count register to re-arm OUT transfers.
•
•
Toggle bits are cleared (11).
The device address is reset to zero (13).
Page 10-6
Chapter 10. EZ-USB Resets
EZ-USB TRM v1.9
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