6.16 The Autopointer
Bulk endpoint data is available in 64-byte buffers in EZ-USB RAM. In some cases it is
preferable to access bulk data as a FIFO register rather than as a RAM. The EZ-USB core
provides a special data pointer which automatically increments when data is transferred.
Using this Autopointer, the 8051 can access any contiguous block of internal EZ-USB
RAM as a FIFO.
AUTOPTRH
Autopointer Address High
7FE3
b7
b6
b5
b4
b3
b2
b1
b0
A15
A14
A13
A12
A11
A10
A9
A8
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
AUTOPTRL
Autopointer Address Low
7FE4
b7
b6
b5
b4
b3
b2
b1
b0
A7
A6
A5
A4
A3
A2
A1
A0
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
AUTODATA
Autopointer Data
7FE5
b7
b6
b5
b4
b3
b2
b1
b0
D7
D6
D5
D4
D3
D2
D1
D0
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
R/W
x
Figure 6-12. Autopointer Registers
The 8051 first loads AUTOPTRH and AUTOPTRL with a RAM address (for example the
address of a bulk endpoint buffer). Then, as the 8051 reads or writes data to the data reg-
ister AUTODATA, the address is supplied by AUTOPTRH/L, which automatically incre-
ments after every read or write to the AUTODATA register. The AUTOPTRH/L registers
may be written or read at anytime. These registers maintain the current pointer address, so
the 8051 can read them to determine where the next byte will be read or written.
Page 6-22
Chapter 6. EZ-USB CPU
EZ-USB TRM v1.9
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