Draft 6/5/00
A-18
Application Information
Copyright 2000 by LSI Logic Corporation. All rights reserved.
A.11 Serial Port
The L80223 uses an MI serial port to access the device registers. Any
external device that has a IEEE 802.3 compliant MI interface can connect
directly to the L80223 without any glue logic, as shown in
Figure A.1
through
Figure A.3
.
As described earlier, the MI serial port consists of eight signals: MDC,
MDIO, MDINTn, and MDA[4:0]n. However, only two signals, MDC and
MDIO, are needed to shift data in and out. MDA[4:0]n are not needed,
but are provided for convenience only.
Note that the MDA[4:0]n addresses are inverted inside the L80223 before
going to the MI serial port block. This means that the MDAn[4:0] pins
would have to be pin strapped to 0b11111 externally to successfully
match the MI physical address of 0b0000 on the PHYAD[4:0] bits
internally.
A.11.1 Polling and Interrupt
The device status bits can be monitored in one of two ways:
Polling the serial port, or
Responding to interrupts
The polling method reads the registers at regular intervals and compares
the status bits to their previous values to determine any changes. To
make polling simpler, all the registers can be accessed in a single read
or write cycle. To do this, set the register address bits REGAD[4:0] to
0b11111 and add enough clocks to read out all the bits (provided the
multiple register access feature has been enabled).
The interrupt feature detects changes in the status output bits without
register polling. When the device asserts an interrupt, it indicates that
one or more of the status output bits has changed since the last read
cycle. There are three interrupt output indicators on the device:
MDINTn pin assertion
Interrupt pulse on MDIO
INT bit set in the MI serial port Status Output register.