GR740-UM-DS, Nov 2017, Version 1.7 289 www.cobham.com/gaisler
GR740
19.4 8-bit and 16-bit PROM access
The PROM areas can be configured for 8- or 16-bit operation by programming the ROM width field
in the memory configuration register. Since reads to memory are always done on 32-bit word basis,
read access to 8-bit memory will be transformed in a burst of four read cycles while access to 16-bit
memory will generate a burst of two 16-bit reads. During writes, only the necessary bytes will be writ-
ten. Figure 30 shows an interface example with 8-bit PROM. Figure 31 shows an example of a 16-bit
memory interface.
EDAC is not supported for 16-bit wide memories and therefore the EDAC enable bit corresponding to
a 16-bit wide area must not be set.
Figure 28. I/O read cycle (0-waitstates)
data1
promio_addr
ios_n
promio_data
promio_oen
lead-out
clk
A1
D1
lead-in data2
Figure 29. I/O write cycle (0-waitstates)
promio_addr
io_sn
promio_data
promio_wen
lead-out
clk
A1
D1
lead-in
data
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