DM9000A
APPLICATION NOTES
Preliminary 9
Version: DM9000A-AN-V121
November 27, 2007
2.1.3 Command Type
In the DM9000A, there are only two registers, named INDEX port and DATA port, which can
be accessed directly. These two ports are distinguished by the CMD pin in the access
command cycle. When CMD is low in command cycle, INDEX port is accessed; otherwise,
when CMD is high, DATA port is accessed.
All of these control and status registers in the DM9000A are accessed indirectly by the
INDEX/ DATA ports. The command sequence to access the specified control/ status register
is: firstly, to write the register’s address into INDEX port, then read/ write their data through
DATA port. The following diagram (Figure 2.2) is an example for the DM9000A CMD pin
connected to an embedded system.
The DM9000A device INDEX port
= nCS a 0x0
The DM9000A device DATA port
= nCS a 0x4
DM9000A
Processor
SA2
nCS
CMD
CS
Figure 2.2 CMD Pin and Processor Interface.
