DP8344 datasheet(69/184 Pages) NSC

69 / 184 page

40 Remote Interface and Arbitration System (RIAS) (Continued)

TLF9336 – 93

(a) Slow Buffered Write

TLF9336 – 94

(b) Fast Buffered Write

FIGURE 4-10 Buffered Write from Remote Processor

In both Buffered Write Modes XACK is asserted to wait the

RP The Latched Write Mode makes it possible for the RP to

write to the BCP without getting waited The timing for the

Latched Write Mode is shown in

Figure 4-11 When the Re-

mote Processor writes to the BCP its address and data

buses are externally latched on the rising edge of REM-WR

Even though REM-WR has been asserted XACK does not

TLF9336 – 95

FIGURE 4-11 Latched Write from Remote Processor

switch The BCP only begins remote access execution after

the trailing edge of REM-WR Since the RP is not requesting

data back from the BCP it can continue execution without

waiting for the BCP to complete the remote access After

REM-WR is deasserted WR-PEND is taken low to prevent

overwrite of the latches A minimum of two T-states later

LCL switches and AD A and the external address latch go

into TRI-STATE allowing the latches which contain the re-

mote address and data to become active If the RP attempts

to initiate another access before the current write is com-

plete XACK is taken low to wait the RP and the address

and the data are safe because WR-PEND prevents the

latches from opening

The Access Phase ends when

INT-WRITE rises and the data is written One T-state later

LCL falls and one T-state after that WR-PEND rises If an-

other access is pending it can begin in the next T-state

This is indicated by XACK rising when WR-PEND rises

A minimum BCPRP interface utilizes four TRI-STATE buff-

ers or latches A block diagram of this interface is shown in

Figure 4-12 The blocks A B C and D indicate the location

of buffers or latches Blocks A and B isolate 16 bits of the

RP’s address bus from the BCP’s Data Address bus Two

more blocks C and D bidirectionally isolate 8 bits of the

RP’s data bus from the BCP AD bus

DP8344 Datasheet(PDF) 69 Page - National Semiconductor (TI)