DS80C320-MCG Datasheet, PDF (83/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
DATA MEMORY INTERCONNECT
As described in Section 4, the High-Speed Microcontroller provides a small amount of RAM mapped as
registers for on-chip direct access. This is not considered data memory and does not fall into the memory
map. Systems that require more RAM or memory mapped peripherals must use the data memory area.
This segment is a 64KB space located between 0000h and FFFFh. It is reached using the MOVX
instruction. Any use of this instruction automatically accesses the data area. Although, the original 8051
convention placed all data memory off-chip, many members of the High-Speed Microcontroller family
contain some data memory on-chip.
From a software standpoint, the physical location of the data area is not relevant because the same
instructions are used. Like the program segment, if software accesses a data address that is above the on-
chip data area, this access will automatically be routed to the Expanded bus. Thus data or peripherals that
are off-chip can be used in conjunction with on-chip memory by selecting addresses that do not overlap.
As an example, if the microcontroller has 1KB of on-chip data memory, then a MOVX instruction at
location 0400h will be directed off-chip via the Expanded bus.
The physical connection of off-chip data memory is shown in Figure 6-3. This illustrates a DS80C320
with interfaced with an 8K SRAM. The data memory map begins at address 0000h since the DS80C320
has no on-chip data memory. A similar interconnection scheme would be implemented if a device with
internal data memory, such as the DS87C520 would be used. Note that any external memory that
overlapped the range of on-chip data memory would not be used.
PROGRAM MEMORY INTERFACE Figure 6-1
PSEN
ALE
CK
74F373
LATCH
DS80C320
OE
LBS ADDRESS ₍₈₎
DATA BUS
(8)
27C256
32K X 8
EPROM
CE
PORT 2
MSB ADDRESS (7)
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