91C100FDREVB Datasheet, PDF (31/68 Pages) SMSC Corporation – FEAST FAST ETHERNET CONTROLLER WITH FULL DUPLEX CAPABILITY

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 Data Register FIFO is empty. The NOT EMPTY bit of this register
can be read to determine if the 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 a dword aligned value.
BANK 2
OFFSET
8 THROUGH Bh
NAME
DATA REGISTER
TYPE
READ/WRITE
SYMBOL
DATA
DATA HIGH
X
X
X
X
X
X
X
X
DATA LOW
X
X
X
X
X
X
X
X
DATA REGISTER - Used to read or write the data buffer byte/word presently addressed by the pointer register.
This register is mapped into two uni-directional FIFOs that allow moving words to and from the LAN91C100FD regardless
of whether the pointer address is even, odd or dword aligned. Data goes through the write FIFO into memory, and is pre-
fetched from memory into the read FIFO. If byte accesses are used, the appropriate (next) byte can be accessed through
the Data Low or Data High registers. The order to and from the FIFO is preserved. Byte, word and dword accesses can be
mixed on the fly in any order.
This register is mapped into two consecutive word locations to facilitate double word move operations regardless of the
actual bus width (16 or 32 bits). The DATA register is accessible at any address in the 8 through Ah range, while the
number of bytes being transferred is determined by A1 and nBE0-nBE3. The FIFOs are 12 bytes each.
BANK 2
OFFSET
C
NAME
INTERRUPT STATUS REGISTER
TYPE
READ ONLY
SYMBOL
IST
RX_DISC
INT
0
ERCV INT
0
EPH INT
0
RX_OVRN
INT
0
ALLOC INT
0
TX EMPTY
INT
1
TX INT
0
RCV INT
0
SMSC DS – LAN91C100FD REV. B
Page 31
Rev. 05/31/2000