LAN91C100 Datasheet, PDF (40/101 Pages) SMSC Corporation – FEAST™ Fast Ethernet Controller

I/O SPACE - BANK2
OFFSET
6
NAME
POINTER REGISTER
TYPE
READ/WRITE
NOT EMPTY is
a read only bit
SYMBOL
PTR
HIGH
BYTE
RCV
0
AUTO
INCR.
0
READ
0
ETEN
0
NOT
EMPTY
0
POINTER HIGH
0
0
0
LOW
BYTE
POINTER LOW
0
0
0
0
0
0
0
0
POINTER REGISTER The value of this register
determines the address to be accessed within
the transmit or receive areas. It will auto-
increment on accesses to the data register when
AUTO INCR. is set. The increment is by one for
every byte access, by two for every word
access, and by four for every double word
access. When RCV is set, the address refers to
the receive area and uses the output of RX FIFO
as the packet number, when RCV is clear the
address refers to the transmit area and uses the
packet number at the Packet Number Register.
READ Determines the type of access to follow.
If the READ bit is high, the operation intended is
a read. If the READ bit is low, the operation is a
write. Loading a new pointer value, with the
READ bit high, generates a pre-fetch into the
Data Register for read purposes.
Readback of the pointer will indicate the value of
the address last accessed by the CPU (rather
than the last pre-fetched). This allows any
interrupt routine that uses the pointer, to save it
and restore it without affecting the process being
interrupted.
The Pointer Register should not be loaded until
the CPU has verified that the NOT EMPTY bit is
clear to ensure that the Data Register FIFO is
empty. On reads, if IOCHRDY is not connected
to the host, the Data Register should not be
read before 370ns after the pointer was loaded
to allow the Data Register FIFO to fill.
If the pointer is loaded using 8 bit writes, the low
byte should be loaded first and the high byte
last.
ETEN When set, enables EARLY Transmit
underrun detection. Normal operation when
clear.
NOT EMPTY When set, indicates that the Write
Data FIFO is not empty yet. The CPU can verify
that the FIFO is empty before loading a new
pointer value. This is a read only bit.
Note: If AUTO INCR. is not set, the pointer must
be loaded with an even value.
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