Texas Instruments DM648 DSP, TMS320DM647 manual 11 DDR2 Sdram Memory Initialization

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Peripheral Architecture

2.11 DDR2 SDRAM Memory Initialization

DDR2 SDRAM devices contain mode and extended mode registers that configure the mode of operation for the device. These registers control parameters such as burst type, burst length, and CAS latency. The DDR2 memory controller programs the mode and extended mode registers of the DDR2 memory by issuing MRS and EMRS commands during the initialization sequence described in Section 2.11.2 and Section 2.11.3. The initialization sequence performed by the DDR2 memory controller is compliant with the JESDEC79-2A specification.

The DDR2 memory controller performs the initialization sequence under the following conditions:

∙Automatically following a hard or soft reset, see Section 2.11.2.

∙Following a write to the two least-significant bytes in the SDRAM configuration register (SDCFG); see Section 2.11.3.

At the end of the initialization sequence, the DDR2 memory controller performs an auto-refresh cycle, leaving the DDR2 memory controller in an idle state with all banks deactivated.

When the initialization section is started automatically after a hard or soft reset, commands and data stored in the DDR2 memory controller FIFOs are lost. However, when the initialization sequence is initiated by a write to the two least-significant bytes in SDCFG, data and commands stored in the DDR2 memory controller FIFOs are not lost and the DDR2 memory controller ensures read and write commands are completed before starting the initialization sequence.

2.11.1DDR2 SDRAM Device Mode Register Configuration Values

The DDR2 memory controller initializes the mode register and extended mode register 1 of the memory device with the values shown on Table 9 and Table 10. The DDR2 SDRAM extended mode registers 2 and 3 are configured with a value of 0h.

Table 9. DDR2 SDRAM Mode Register Configuration

Mode	Mode Register
Register Bit	Field	Init Value	Description
12	Power-down Mode	0	Active power-down exit time bit. Configured for Fast exit.
11-9	Write Recovery	SDTIM1.T_WR	Write recovery bits for auto-precharge. Initialized using the
			T_WR bits of the SDRAM timing 1 register (SDTIM1).
8	DLL Reset	0	DLL reset bits. DLL is not in reset.
7	Mode	0	Operating mode bit. Normal operating mode is always
			selected.
6-4	CAS Latency	SDCFG.CL	CAS latency bits. Initialized using the CL bits of the SDRAM
			configuration register (SDCFG).
3	Burst Type	0	Burst type bits. Sequential burst mode is always used.
2-0	Burst Length	3h	Bust length bits. A burst length of 8 is always used.

Table 10. DDR2 SDRAM Extended Mode Register 1 Configuration

Mode	Mode Register
Register Bit	Field	Init Value	Description
12	Output Buffer Enable	0	Output buffer enable bits. Output buffer is always enabled.
11	RDQS Enable	0	RDQS enable bits. Always initialized to 0 (RDQS signals
			disabled.)
10	DQS enable	0	DQS enable bit. Always initialized to 0 (DQS signals
			enabled.)
9-7	OCD Operation	0h	Off-chip driver impedance calibration bits. This bit is always
			initialized to 0h.
6	ODT Value (Rtt)	0	On-die termination effective resistance (Rtt) bit. Together
			with bit 2, this bit selects the value for Rtt as 75Ω.
5-3	Additive Latency	0h	Additive latency bits. Always initialized to 0h (no additive
			latency).
SPRUEK5A –October 2007			DSP DDR2 Memory Controller	27
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