dp83901a National Semiconductor Corporation, dp83901a Datasheet - Page 42

• Manufacturer Part Number: dp83901a
• Description: Serial Network Interface Controller
• 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-
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
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
Bus Handshake Signals for Remote DMA Transfers
(Continued)
42
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)
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
TL F 10469 – 27
TL F 10469 – 28