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Boot Loader
4-15
Memory and I/O Spaces
4.5.2 Connecting the EPROM to the Processor
To map the EPROM into the global data space at address 8000h, make the
following connections between the processor and the EPROM (refer to
Figure 4–8):
Connect the address lines of the processor and the EPROM (see lines
A14–A0 in the figure).
Connect the data lines of the processor and the EPROM (see lines D7–D0
in the figure).
Connect the processor’s RD pin to the EPROM’s output enable pin (OE
in the figure).
Connect the processor’s BR pin to the EPROM’s chip enable pin (CE in
the figure).
Notes:
1) If the EPROM is smaller than 32K words × 8 bits, connect only the ad-
dress pins that are available on the EPROM.
2) When the boot loader accesses global memory, along with BR
, DS is
driven low. Design your system such that the DS
signal does not initiate
undesired accesses to data memory during the boot loads.
Figure 4–8. Connecting the EPROM to the Processor
EPROM
D7–D0D7–D0
’C2xx
A14–A0 A14–A0
OE
CE
RD
BR
(27C256)
8
15