Intel® PXA255 Processor Developer’s Manual 6-61

Memory Controller
6.8.2 Expansion Memory Configuration Register (MECR)

To eliminate external hardware, the two bits in MECR, shown in Table 6- 27, 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/wri te register. Ignore reads from reserved bit s. Write zeros to res erved bits.
11101 29 31 61 62 92 93
11110 30 32 63 64 9 5 96
11111 31 33 65 66 9 8 99

Table 6-26. 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 6-27. 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
CIT
NOS
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
1CIT
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.
0NOS
Number-of-Sockets
0 – 1 Socket
1 – 2 Sockets