Cirrus Logic EP73xx - Manual (Page 84)

7-4 EP7309/11/12 User’s Manual - DS508UM4

Copyright Cirrus Logic, Inc. 2003
SDRAM Controller
7
SDWIDTH[1:0]: The width of each SDRAM device:
00 = 4 bits
01 = 8 bits
10 = 16 bits
11 = 32 bits
This value is independent of the bus width setting and is
necessary to differentiate the individual devices within a bank.
CLKCTL: Control over the SDRAM clock:
0 = SDRAM clock is permanently enabled except when in standby
mode.
1 = SDRAM clock stops when the EP73xx is put into the
STANDBY state or SDACTIVE = ‘0’.
There will be an additional delay of one clock cycle for any access
request made when the SDRAM clock is stopped.
SDACTIVE: Enables the SDRAM controller:
0 = Disable SDRAM controller
1 = Enable SDRAM controller
The default state is ‘0’.
SDRAM Refresh Period Register (SDRFPR)
Address: 0x80002340, Read / Write
Definition: SDRFPR is a register containing a 16-bit value representing the
interval between SDRAM refresh commands. The value
programmed is in bus clock cycles. The following example
calculates the value for REFRATE for a 16
µS refresh period with a
bus clock of 36 MHz:
16E
-6
* 36E
6
= 576
The refresh timer is set to 256 by nPOR to ensure a refresh time of
better than 16
µS even at 13 MHz. This register should not be
programmed to a value below 2. Otherwise, the bus may become
locked.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
RSVD
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
REFRATE