SMC91C100 Datasheet, PDF (39/83 Pages) List of Unclassifed Manufacturers – FEAST Fast Ethernet Controller

I/O SPACE - BANK2
OFFSET
6
HIGH
BYTE
RCV
0
NAME
POINTER REGISTER
AUTO
INCR.
0
READ
0
ETEN
0
TYPE
READ/WRITE
NOT EMPTY is a
read only bit
SYMBOL
PTR
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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