2 expansion memory configuration register (mecr), Expansion memory configuration register (mecr) -63, Mecr bit definition -63 – Intel PXA255 User Manual
Page 245
Intel® PXA255 Processor Developer’s Manual
6-63
Memory Controller
6.8.2
Expansion Memory Configuration Register (MECR)
To eliminate external hardware, the two bits in MECR, shown in
, are used to signal the
memory controller when a card (16-Bit PC Card/Compact Flash) is inserted in the socket and the
number of cards supported in the system. The number-of-sockets bit is required because the
PSKTSEL pin is used as the nOE for the data transceivers in single socket mode. The card-is-there
bit is used to reduce external hardware by ignoring nIOIS16 and nPWAIT when there is no card
inserted in the socket.
This is a read/write register. Ignore reads from reserved bits. Write zeros to reserved bits.
11101
29
31
61
62
92
93
11110
30
32
63
64
95
96
11111
31
33
65
66
98
99
Table 6-29. Card Interface Command Assertion Code Table
MCMEMx_ASST
MCATTx_ASST
MCIOx_ASST
x_ASST_WAIT
x_ASST_HOLD
x_ASST_WAIT +
x_ASST_HOLD
(nPIOW asserted) (nPIOR asserted) (nPIOW asserted) (nPIOR asserted)
Programmed
Bit Value
Code
decimal
value
# MEMCLKs
(minimum)
to wait before
checking for
nPWAIT=’1’
# MEMCLKs
(minimum)
to assert
command
(nPIOW) after
nPWAIT=’1’
# MEMCLKs
(minimum)
to assert
command
(nPIOR) after
nPWAIT=’1’
# MEMCLKs
(minimum)
command
assertion time
# MEMCLKs
(minimum)
command
assertion time
(Code)
(Code)
(Code + 2)
(2*Code + 3)
(2*Code + 4)
(3*Code + 5)
(3*Code + 6)
Table 6-30. MECR Bit Definition
4800_0014
MECR
Memory Controller
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
reserved
CI
T
NO
S
Reset 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Bits
Name
Description
31:2
—
reserved
1
CIT
Card-Is-There
0 – No card inserted
1 – Card inserted
Must be set by software when at least one card is present and must be cleared when all
cards are removed.
0
NOS
Number-of-Sockets
0 – 1 Socket
1 – 2 Sockets