HPC16004 datasheet(25/36 Pages) NSC

25 / 36 page

Shared Memory Support

Shared memory access provides a rapid technique to ex-

change data It is effective when data is moved from a pe-

ripheral to memory or when data is moved between blocks

of memory A related area where shared memory access

proves effective is in multiprocessing applications where

two CPUs share a common memory block The HPC46064

supports shared memory access with two pins The pins are

the RDYHLD input pin and the HLDA output pin The user

can software select either the Hold or Ready function by the

state of a control bit The HLDA output is multiplexed onto

port B

The host uses DMA to interface with the HPC46064 The

host initiates a data transfer by activating the HLD input of

the HPC46064 In response the HPC46064 places its sys-

tem bus in a TRI-STATE Mode freeing it for use by the host

The host waits for the acknowledge signal (HLDA) from the

HPC46064 indicating that the sytem bus is free On receiv-

ing the acknowledge the host can rapidly transfer data into

or out of the shared memory by using a conventional DMA

controller Upon completion of the message transfer the

host removes the HOLD request and the HPC46064 re-

sumes normal operations

To insure proper operation the interface logic shown is rec-

ommended as the means for enabling and disabling the us-

er’s bus

Figure 28 illustrates an application of the shared

memory interface between the HPC46064 and a Series

32000 system

TLDD11372 26

FIGURE 28 Shared Memory Application HPC46064 Interface to Series 32000 System

HPC16004 Datasheet(PDF) 25 Page - National Semiconductor (TI)