Texas Instruments TMS320DM643 manual Configuring Sdram Timing Registers Sdtimr and SDTIMR2

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Supported Use Cases

3.2.3Configuring SDRAM Timing Registers (SDTIMR and SDTIMR2)

The SDRAM timing register (SDTIMR) and SDRAM timing register 2 (SDTIMR2) configure the DDR2 memory controller to meet the data sheet timing parameters of the attached DDR2 device. Each field in SDTIMR and SDTIMR2 corresponds to a timing parameter in the DDR2 data sheet specification. Table 19 and Table 20 display the register field name and corresponding DDR2 data sheet parameter name along with the data sheet value. These tables also provide a formula to calculate the register field value and displays the resulting calculation. Each of the equations include a minus 1 because the register fields are defined in terms of DDR2 clock cycles minus 1. See Section 4.4 and Section 4.5 for more information.

Table 19. SDRAM Timing Register (SDTIMR) Configuration

	DDR2 Data
Register Field	Manual		Data Manual	Formula	Register
Name	Parameter Name	Description	Value (nS)	(Register field must be ≥)	Value
T_RFC	tRFC	Refresh cycle time	127.5	(tRFC × fDDR2_CLK) - 1	16
T_RP	tRP	Precharge command to	20	(tRP × fDDR2_CLK) - 1	2
		refresh or activate
		command
T_RCD	tRCD	Activate command to	20	(tRCD × fDDR2_CLK) - 1	2
		read/write command
T_WR	tWR	Write recovery time	15	(tWR × fDDR2_CLK) - 1	1
T_RAS	tRAS	Active to precharge	45	(tRAC × fDDR2_CLK) - 1	5
		command
T_RC	tRC	Activate to Activate	65	(tRC × fDDR2_CLK) - 1	8
		command in the same
		bank
T_RRD	tRRD	Activate to Activate	10	((4 × tRRD) + (2 × tCK))/(4 × tCK) - 1	1
		command in a different
		bank
T_WTR	tWTR	Write to read command	10	(tWTR × fDDR2_CLK) - 1	1
		delay

Note: The equation given above for the T_RRD field applies only for 8 bank DDR2 memories. When interfacing to DDR2 memories with less than 8 banks, the T_RRD field should be calculated using the following equation (tRRD × fDDR2_CLK) - 1.

Table 20. SDRAM Timing Register 2 (SDTIMR2) Configuration

	DDR2 Data
Register Field	Manual		Data Manual	Formula (Register	Register
Name	Parameter Name	Description	Value	field must be ≥)	Value
T_XSNR	tXSNR	Exit self refresh to a non-read	137.5 nS	(tXSNR × fDDR2_CLK) - 1	18
		command
T_XSRD	tXSRD	Exit self refresh to a read	200 (tCK cycles)	tXSRD - 1	199
		command
T_RTP	tRTP	Read to precharge command delay	7.5 nS	(tRTP × fDDR2_CLK) - 1	1
T_CKE	tCKE	CKE minimum pulse width	3 (tCK cycles)	tCKE - 1	2

SPRU986B–November 2007	DDR2 Memory Controller	39
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