DP8390 NSC [National Semiconductor], DP8390 Datasheet - Page 36

• Manufacturer Part Number: DP8390
• Description: NIC Network Interface Controller
• Manufacturer: NSC [National Semiconductor]

13 0 Bus Arbitration and Timing
REMOTE READ TIMING
1) The DMA reads byte word from local buffer memory and
2) A Request Line (PRQ) is asserted to inform the system
3) The system reads the port the read strobe (RACK) is
REMOTE WRITE TIMING
A Remote Write operation transfers data from the I O port
to the local buffer RAM The NIC initiates a transfer by re-
questing a byte word via the PRQ The system transfers a
byte word to the latch via IOW this write strobe is detected
by the NIC and PRQ is removed By removing the PRQ the
Remote DMA holds off further transfers into the latch until
the current byte word has been transferred from the latch
PRQ is reasserted and the next transfer can begin
writes byte word into latch increments the DMA address
and decrements the byte count (RBCR0 1)
that a byte is available
used as an acknowledge by the Remote DMA and it goes
back to step 1
(Continued)
36
Note that in order for the Remote DMA to transfer a byte
from memory to the latch it must arbitrate access to the
local bus via a BREQ BACK handshake After each byte or
word is transferred to the latch BREQ is dropped If a Local
DMA is in progress the Remote DMA is held off until the
local DMA is complete
1) NIC asserts PRQ System writes byte word into latch
2) Remote DMA reads contents of port and writes
3) Go back to step 1
Steps 1– 3 are repeated until the remote DMA is com-
plete
NIC removes PRQ
byte word to local buffer memory increments address
and decrements byte count (RBCR0 1)
Steps 1– 3 are repeated until the remote DMA is com-
plete
TL F 8582 – 73
TL F 8582– 72