AMD Elan SC520, User Manual, Page: 241 / 444

ROM/Flash Controller
Élan™SC520 Microcontroller User’s Manual 12-11
Figure 12-9 Page Access for Fetching Two Doublewords from a 16-Bit ROM
12.5.3.3 Cache-Line Fill
If a memory section is accessed that is cacheable, the ken signal is asserted to the Am5
x
86
CPU indicating a cache-line fill operation. This causes the Am5
x
86 CPU to read four
doublewords (16 bytes) and leads to multiple ROM accesses. A cache-line fill to a 32-bit
ROM is depicted in Figure 12-10.
Figure 12-10 Cache-Line Fill (Fetching Four Doublewords from a 32-Bit ROM)
12.5.3.4 Writing to Flash Devices
The ÉlanSC520 microcontroller supports writable Flash devices. Since Flash devices are
not intended for random write accesses, no burst-write operations are supported, i.e., rdy
is returned to the Am5
x
86 CPU. Figure 12-11 shows a write cycle to a Flash ROM. In
addition, for write accesses, the ROM controller bus-sizes ROM accesses to indicate the
start cycle
- - - C
0 2 0 2
- - - 8
CPU clock
ads
GPA25–GPA2
GPA1–GPA0
GPD15–GPD0, or
brdy
blast
BOOTCS
ROMRD
MD15–MD0
- - - C - - - 8 - - - 4
- - - 0
CPU clock
ads
ken
GPA25–GPA0
MD31–MD0
brdy
blast
BOOTCS
ROMRD