GR740-UM-DS, Nov 2017, Version 1.7
288
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GR740
19.3
Memory mapped IO
Accesses to IO have similar timing as PROM accesses. The IO select (IO_SN) and output enable
(PROMIO_OEN) signals are delayed one clock to provide stable address before IO_SN is asserted.
All accesses are performed as non-consecutive accesses as shown in figure 28. The data2 phase is
extended when waitstates are added.
Figure 26.
Prom write cycle (0-waitstates)
data
promio_addr
prom_cen
promio_data
promio_wen
lead-out
clk
A1
D1
lead-in
Figure 27.
Prom write cycle (2-waitstates)
data
promio_addr
prom_cen
promio_data
promio_wen
lead-out
clk
A1
D1
lead-in
data
data