Texas Instruments SM320F2812-HT specifications Xintf Signal Alignment to Xclkout, Xr/W

SM320F2812-HT

www.ti.com SGUS062A –JUNE 2009 –REVISED APRIL 2010

6.22 XINTF Signal Alignment to XCLKOUT

For each XINTF access, the number of lead, active, and trail cycles is based on the internal clock XTIMCLK. Strobes such as XRD, XWE, and zone chip-select (XZCS) change state in relationship to the rising edge of XTIMCLK. The external clock, XCLKOUT, can be configured to be either equal to or one-half the frequency of XTIMCLK.

For the case where XCLKOUT = XTIMCLK, all of the XINTF strobes changes state with respect to the rising edge of XCLKOUT. For the case where XCLKOUT = one-half XTIMCLK, some strobes change state either on the rising edge of XCLKOUT or the falling edge of XCLKOUT. In the XINTF timing tables, the notation XCOHL is used to indicate that the parameter is with respect to either case; XCLKOUT rising edge (high) or XCLKOUT falling edge (low). If the parameter is always with respect to the rising edge of XCLKOUT, the notation XCOH is used.

For the case where XCLKOUT = one-half XTIMCLK, the XCLKOUT edge with which the change is aligned can be determined based on the number of XTIMCLK cycles from the start of the access to the point at which the signal changes. If this number of XTIMCLK cycles is even, the alignment is with respect to the rising edge of XCLKOUT. If this number is odd, then the signal changes with respect to the falling edge of XCLKOUT. Examples include the following:

•Strobes that change at the beginning of an access always align to the rising edge of XCLKOUT. This is because all XINTF accesses begin with respect to the rising edge of XCLKOUT.

Examples:	XZCSL	Zone chip-select active low
	XRNWL		active low
		XR/W

•Strobes that change at the beginning of the active period aligns to the rising edge of XCLKOUT if the total number of lead XTIMCLK cycles for the access is even. If the number of lead XTIMCLK cycles is odd, then the alignment is with respect to the falling edge of XCLKOUT.

Examples:	XRDL	XRD active low
	XWEL		active low
		XWE

•Strobes that change at the beginning of the trail period aligns to the rising edge of XCLKOUT if the total number of lead + active XTIMCLK cycles (including hardware waitstates) for the access is even. If the number of lead + active XTIMCLK cycles (including hardware waitstates) is odd, then the alignment is with respect to the falling edge of XCLKOUT.

Examples:	XRDH	XRD inactive high
	XWEH		inactive high
		XWE

•Strobes that change at the end of the access aligns to the rising edge of XCLKOUT if the total number of lead + active + trail XTIMCLK cycles (including hardware waitstates) is even. If the number of lead + active + trail XTIMCLK cycles (including hardware waitstates) is odd, then the alignment is with respect to the falling edge of XCLKOUT.

Examples:	XZCSH	Zone chip-select inactive high
	XRNWH		inactive high
		XR/W

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