Texas Instruments TMS320C642x DSP manual Sdram Timing Register Sdtimr

www.ti.com

DDR2 Memory Controller Registers

4.4SDRAM Timing Register (SDTIMR)

The SDRAM timing register (SDTIMR) configures the DDR2 memory controller to meet many of the AC timing specification of the DDR2 memory. The SDTIMR register is programmable only when the TIMUNLOCK bit is set to 1 in the SDBCR. Note that DDR_CLK is equal to the period of the DDR_CLK signal. See the DDR2 memory data sheet for information on the appropriate values to program each field. The SDTIMR is shown in Figure 22 and described in Table 28.

Figure 22. SDRAM Timing Register (SDTIMR)

31			25	24	22	21	19	18		16
	T_RFC				T_RP		T_RCD		T_WR
	R/W-1Ah				R/W-5h		R/W-5h		R/W-3h
15	11	10			6	5	3	2	1	0
	T_RAS			T_RC			T_RRD	Rsvd	T_WTR
	R/W-9h			R/W-Eh			R/W-3h	R-0	R/W-3h

LEGEND: R/W = Read/Write; R = Read only; -n= value after reset

Table 28. SDRAM Timing Register (SDTIMR) Field Descriptions

Bit	Field	Value	Description
31-25	T_RFC	0-7Fh	Specifies the minimum number of DDR_CLK cycles from a refresh or load mode command to a refresh
			or activate command, minus 1. Corresponds to the trfc AC timing parameter in the DDR2 data sheet.
			Calculate by:
			T_RFC = (trfc/DDR_CLK period) - 1
24-22	T_RP	0-7h	Specifies the minimum number of DDR_CLK cycles from a precharge command to a refresh or activate
			command, minus 1. Corresponds to the trp AC timing parameter in the DDR2 data sheet. Calculate by:
			T_RP = (trp/DDR_CLK period) - 1
21-19	T_RCD	0-7h	Specifies the minimum number of DDR_CLK cycles from an activate command to a read or write
			command, minus 1. Corresponds to the trcd AC timing parameter in the DDR2 data sheet. Calculate by:
			T_RCD = (trcd/DDR_CLK period) - 1
18-16	T_WR	0-7h	Specifies the minimum number of DDR_CLK cycles from the last write transfer to a precharge
			command, minus 1. Corresponds to the twr AC timing parameter in the DDR2 data sheet. Calculate by:
			T_WR = (twr/DDR_CLK period) - 1
			When the value of this field is changed from its previous value, the initialization sequence will begin.
15-11	T_RAS	0-1Fh	Specifies the minimum number of DDR_CLK cycles from an activate command to a precharge
			command, minus 1. Corresponds to the tras AC timing parameter in the DDR2 data sheet. Calculate by:
			T_RAS = (tras/DDR_CLK period) - 1
			T_RAS must be greater than or equal to T_RCD.
10-6	T_RC	0-1Fh	Specifies the minimum number of DDR_CLK cycles from an activate command to an activate
			command, minus 1. Corresponds to the trc AC timing parameter in the DDR2 data sheet. Calculate by:
			T_RC = (trc/DDR_CLK period) - 1
5-3	T_RRD	0-7h	Specifies the minimum number of DDR_CLK cycles from an activate command to an activate command
			in a different bank, minus 1. Corresponds to the trrd AC timing parameter in the DDR2 data sheet.
			Calculate by:
			T_RRD = (trrd/DDR_CLK period) - 1
			Note: for an 8 bank DDR2 device this field must be equal to ((4 × tRRD) + (2 × tCK)) / (4 × tCK) - 1.
2	Reserved	0	Reserved
1-0	T_WTR	0-3h	Specifies the minimum number of DDR_CLK cycles from the last write to a read command, minus 1.
			Corresponds to the twtr AC timing parameter in the DDR2 data sheet. Calculate by:

T_WTR = (twtr/DDR_CLK period) - 1

46 DDR2 Memory Controller SPRUEM4A–November 2007

Submit Documentation Feedback