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SAM9G45 [DATASHEET]
6438K–ATARM–12-Feb-13
22.4.2
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.
2.
Program the features of the low-power DDR1-SDRAM device into the Configuration Register: asynchro-
3.
Program temperature compensated self refresh (tcr), Partial array self refresh (pasr) and Drive strength
4.
An NOP command will be issued to the low-power DDR1-SDRAM. Program NOP command into the
254). Perform a write access to any DDR1-SDRAM address to acknowledge this command. Now clocks
which drive DDR1-SDRAM device are enabled.
A minimum pause of 200 μs 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 pre-
charge command into the Mode Register, the application must set Mode to 2 in the Mode Register (See
acknowledge this command
6.
Two auto-refresh (CBR) cycles are provided. Program the auto refresh command (CBR) into the Mode
form a write access to any low-power DDR1-SDRAM location twice to acknowledge these commands.
7.
An Extended Mode Register set (EMRS) cycle is issued to program the low-power DDR1-SDRAM param-
eters (TCSR, PASR, DS). The application must set Mode to 5 in the Mode Register (see
Section 22.8.1 onpage 254) and perform a write access to the 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
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 set Mode to 3 in the Mode Register
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. The application must go into Nor-
write access at any location in the low-power DDR1-SDRAM to acknowledge this command.
9.
Perform a write access to any low-power DDR1-SDRAM address.
10. Write the refresh rate into the count field in the DDRSDRC Refresh Timer register (see
page 255).
(Refresh rate = delay between refresh cycles). The low-power DDR1-SDRAM device requires a refresh
every 15.625 μs or 7.81 μs. 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
11. After initialization, the low-power DDR1-SDRAM device is fully functional.