Motorola MVME172 - Manual (Page 228)

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MC2 Chip
3
ROM0 Refer to the table on the Local Bus Memory Map, Note 1,
in Chapter 1.
Flash Access Time Control Register
The MVME172 is populated with a 120ns Flash memory device. Due to
the wide range of Flash speeds, the contents can be changed by software to
adjust for a specific speed.
FWEN Flash write enable function is internal to the ASIC for the
MC2 chip. FWEN set to a 1 enables writes to the Flash
memory space. FWEN set to a 0 inhibits writes to the
Flash memory but the cycle completes without exception.
FT2-FT0 Flash memory access time is controlled by the state of
FT2-FT0. The following table defines the FT2-FT0
encoding (for the MVE172, whose bus frequency is
1 / 2 the
processor frequency, only the 33MHz column applies).
ADR/SIZ $FFF42040 (8 bits)
BIT 15 14 13 12 11 10 9 8
NAME FWEN FT2 FT1 FT0
OPER R R R R R/W R/W R/W R/W
RESET 0 0 0 0 0 1 PL 1 PL 1 PL
FT2-
FT0
Flash Access <= N
at 25 MHz where N =
Flash Access <= N
at 33 MHz where N =
$0 60 ns 40 ns
$1 100 ns 70 ns
$2 140 ns 100 ns
$3 180 ns 130 ns
$4 220 ns 160 ns
$5 260 ns 190 ns
$6 300 ns 210 ns
$7 340 ns 240 ns