Техническая Спецификация для Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK
Модели
AT91SAM9X25-EK
432
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
30.4 Initialization Sequence
The addresses given are for example purposes only. The real address depends on implementation in the product.
30.4.1 SDR-SDRAM Initialization
The initialization sequence is generated by software. The SDR-SDRAM devices are initialized by the following sequence:
1.
Program the memory device type into the Memory Device Register (see
).
2.
Program the features of the SDR-SDRAM device into the Timing Register (asynchronous timing (trc, tras, etc.)),
and into the Configuration Register (number of columns, rows, banks, cas latency) (see
and into the Configuration Register (number of columns, rows, banks, cas latency) (see
and
3.
For low-power SDRAM, temperature-compensated self refresh (TCSR), drive strength (DS) and partial array self
refresh (PASR) must be set in the Low-power Register (see
refresh (PASR) must be set in the Low-power Register (see
A minimum pause of 200 µs is provided to precede any signal toggle.
4.
A NOP command is issued to the SDR-SDRAM. Program NOP command into Mode Register, the application must
set Mode to 1 in the Mode Register (See
set Mode to 1 in the Mode Register (See
SDRAM address to acknowledge this command. Now the clock which drives SDR-SDRAM device is enabled.
5.
An all banks precharge command is issued to the SDR-SDRAM. Program all banks precharge command into
Mode Register, the application must set Mode to 2 in the Mode Register (See
Mode Register, the application must set Mode to 2 in the Mode Register (See
form a write access to any SDR-SDRAM address to acknowledge this command.
6.
Eight auto-refresh (CBR) cycles are provided. Program the auto refresh command (CBR) into Mode Register, the
application must set Mode to 4 in the Mode Register (see
application must set Mode to 4 in the Mode Register (see
).Performs a write access to
any SDR-SDRAM location eight times to acknowledge these commands.
7.
A Mode Register set (MRS) cycle is issued to program the parameters of the SDR-SDRAM devices, in particular
CAS latency and burst length. The application must set Mode to 3 in the Mode Register (see
CAS latency and burst length. The application must set Mode to 3 in the Mode Register (see
) and perform a write access to the SDR-SDRAM to acknowledge this command. The write address must
be chosen so that BA[1:0] are set to 0. For example, with a 16-bit 128 MB SDR-SDRAM (12 rows, 9 columns, 4
banks) bank address, the SDRAM write access should be done at the address 0x20000000.
banks) bank address, the SDRAM write access should be done at the address 0x20000000.
Note:
This address is for example purposes only. The real address is dependent on implementation in the product.
8.
For low-power SDR-SDRAM initialization, an Extended Mode Register set (EMRS) cycle is issued to program the
SDR-SDRAM parameters (TCSR, PASR, DS). The application must set Mode to 5 in the Mode Register (see
SDR-SDRAM parameters (TCSR, PASR, DS). The application must set Mode to 5 in the Mode Register (see
) and perform a write access to the SDR-SDRAM to acknowledge this command. The write
address must be chosen so that BA[1] is set to 1 and BA[0] is set to 0. For example, with a 16-bit 128 MB SDRAM,
(12 rows, 9 columns, 4 banks) bank address the SDRAM write access should be done at the address 0x20800000.
(12 rows, 9 columns, 4 banks) bank address the SDRAM write access should be done at the address 0x20800000.
9.
The application must go into Normal Mode, setting Mode to 0 in the Mode Register (see
10. Write the refresh rate into the count field in the DDRSDRC Refresh Timer register (see
). (Refresh rate =
delay between refresh cycles). The SDR-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
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.
30.4.2 Low-power DDR1-SDRAM Initialization
The initialization sequence is generated by software. The low-power DDR1-SDRAM devices are initialized by the
following sequence:
following sequence:
1.
Program the memory device type into the Memory Device Register (see
).
2.
Program the features of the low-power DDR1-SDRAM device into the Configuration Register: asynchronous tim-
ing (trc, tras, etc.), number of columns, rows, banks, cas latency. See
ing (trc, tras, etc.), number of columns, rows, banks, cas latency. See
.
3.
Program temperature compensated self refresh (tcr), Partial array self refresh (pasr) and Drive strength (ds) into
the Low-power Register. See
the Low-power Register. See