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PAL20LB
Decode and DMA Interface Logic for the DPB39EB
DECODEl
A9 AB A7 AS A5 A4 PCRST INMRD NAl3 IIORD IIOWR GND
PRQ IDACK IWAIT AEN lRACK IWACK ICSX ICSN INICRST ICSROM lACK VCC
CSN = IAEN* A9* AB* IA7* IAS* IA5* IA4* 10WR +
IAEN* A9* AB* IA7* IAS* IA5* IA4* lORD
NICRST = PCRST
RACK = IAEN* A9* AB* IA7* IAS* IA5* A4* PRQ* lORD +
DACK* lORD
WACK = IAEN* A9* AB* IA7* IAS* IA5* A4* PRQ* 10WR +
DACK* 10WR
CSX = CSN* lORD +
CSN* 10WR +
IAEN* A9* AB* IA7* IAS* IA5* A4* lORD +
IAEN* A9* AB* IA7* IAS* IA5* A4* 10WR +
IF (CSX)
WAIT = lACK * CSN +
IPRQ * ICSN
CSROM = INAl3 * NMRD
DESCRIPTION
This PAL performs the 110 decodes for selecting the NIC,
and the handshake signals for NIC's remote DMA. The PAL
supports the DMA channels of the PC for remote DMA
transfers with the NIC and also allows the use of string I/O
between 80286 PC's and NIC's remote DMA.
DECODE1 fixes the I/O BASE of the card at 300h. NIC
registers fall in the space 300h-30fh. To use the string I/O
port, reads and writes are done to port 310h.
Wait states are inserted (WAIT) to the PC bus when register
accesses are given and the NIC is busy performing DMA
operations. When the NIC is ready, / ACK is given and no
(more) wait states are inserted.
Wait states may also be inserted during remote DMA opera·
tions and 80286 machines using string I/O's. WAIT occurs
during a remote read if the PC AT's /IORD goes low before
the DP8390's PRO goes high. Similarly, WAIT occurs during
a remote write if the PC AT's /IOWR goes low before the
NIC's PRO goes high.
NIC registers are accessed when CSN (Chip Select NIC) is
asserted. The lORD and 10WR terms are included to ensure
that the address lines are valid when CSN is given.
The RACK and WACK Signals are used by the NIC's remote
DMA channel to acknowledge the end of a single read or
write operation through the remote DMA I/O ports. These
ports are addressable by the PC DMA channel with DACK
and lORD or 10WR, or by addressing the I/O location 310h
(with string I/O's).
CSX is used to enable the TRI·STATE output of WAIT dur·
ing a register access CSN), and during string I/O to the
remote DMA's I/O port (CSX).
CSROM provides address decode for the address PROM.
The card's unique Ethernet address is transferred to the
system using the NIC's remote DMA.
II
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