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SAM9G46
10. Write the refresh rate into the count field in the DDRSDRC Refresh Timer register (see
page 265). (Refresh rate = delay between refresh cycles). The SDR-SDRAM device
requires a refresh every 15.625 s or 7.81 s. With a 100 MHz frequency, the refresh
timer count register must to be set with (15.625 /100 MHz) = 1562 i.e. 0x061A or (7.81
/100 MHz) = 781 i.e. 0x030d
After initialization, the SDR-SDRAM device is fully functional.
22.3.2
Low-power DDR1-SDRAM Initialization
The initialization sequence is generated by software. The low-power DDR1-SDRAM devices are
initialized by the following sequence:
1.
Program the memory device type into the Memory Device Register (see
Section 22.7.82.
Program the features of the low-power DDR1-SDRAM device into the Configuration
Register: asynchronous timing (trc, tras, etc.), number of columns, rows, banks, cas
3.
Program temperature compensated self refresh (tcr), Partial array self refresh (pasr)
4.
An NOP command will be issued to the low-power DDR1-SDRAM. Program NOP com-
mand into the Mode Register, the application must set Mode to 1 in the Mode Register
address to acknowledge this command. Now clocks which drive DDR1-SDRAM device
are enabled.
A minimum pause of 200 s will be provided to precede any signal toggle.
5.
An all banks precharge command is issued to the low-power DDR1-SDRAM. Program
all banks precharge command into the Mode Register, the application must set Mode to
any low-power DDR1-SDRAM address to acknowledge this command
6.
Two auto-refresh (CBR) cycles are provided. Program the auto refresh command
(CBR) into the Mode Register, the application must set Mode to 4 in the Mode Register
SDRAM location twice to acknowledge these commands.
7.
An Extended Mode Register set (EMRS) cycle is issued to program the low-power
DDR1-SDRAM parameters (TCSR, PASR, DS). The application must set Mode to 5 in
SDRAM to acknowledge this command. The write address must be chosen so that
BA[1] is set to 1 BA[0] is set to 0. For example, with a 16-bit 128 MB SDRAM (12 rows,
9 columns, 4 banks) bank address, the low-power DDR1-SDRAM write access should
be done at the address 0x20800000.
Note:
This address is for example purposes only. The real address is dependent on implementation in
the product.
8.
A Mode Register set (MRS) cycle is issued to program the parameters of the low-power
DDR1-SDRAM devices, in particular CAS latency, burst length. The application must
write access to the low-power DDR1-SDRAM to acknowledge this command. The write
address must be chosen so that BA[1:0] bits are set to 0. For example, with a 16-bit 128
MB low-power DDR1-SDRAM (12 rows, 9 columns, 4 banks) bank address, the
SDRAM write access should be done at the address 0x20000000