dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 46

• Manufacturer Part Number: dp83902a
• Description: St-nictm Serial Network Interface Controller For Twisted Pair
• Manufacturer: National Semiconductor Corporation

13 0 Bus Arbitration and Timing
REMOTE DMA-BIDIRECTIONAL PORT CONTROL
The Remote DMA transfers data between the local buffer
memory and a bidirectional port (memory to I O transfer)
This transfer is arbited on a byte by byte basis versus the
burst transfer used for Local DMA transfers This bidirec-
tional port is also read written by the host All transfers
through this port are asynchronous At any one time trans-
fers are limited to one direction either from the port to local
buffer memory (Remote Write) or from local buffer memory
to the port (Remote Read)
Bus Handshake Signals for Remote DMA Transfers
TL F 11157 – 28
(Continued)
46
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
Steps 1 – 3 are repeated until the remote DMA is complete
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
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
TL F 11157 – 29