hpc36164 National Semiconductor Corporation, hpc36164 Datasheet - Page 28

• Manufacturer Part Number: hpc36164
• Description: High-performance Microcontroller With A/d
• Manufacturer: National Semiconductor Corporation

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 HPC46164
supports shared memory access with two pins The pins are
the RDY HLD 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 HPC46164 The
host initiates a data transfer by activating the HLD input of
FIGURE 29 Shared Memory Application HPC46164 Interface to Series 32000 System
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the HPC46164 In response the HPC46164 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
HPC46164 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 HPC46164 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 29 illustrates an application of the shared
memory interface between the HPC46164 and a Series
32000 system
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