Texas Instruments Digital Signal Processor SM320F2812-HT - Manual (Page 118)

SM320F2812-HT
SGUS062B – JUNE 2009 – REVISED JUNE 2011 www.ti.com
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 XR/W active low
• 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 XWE active low
• 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 XWE inactive high
• 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 XR/W inactive high
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