SMJ34020A Datasheet, PDF (70/92 Pages) Texas Instruments – GRAPHICS SYSTEM PROCESSOR

SMJ34020A
GRAPHICS SYSTEM PROCESSOR
SGUS011B – APRIL 1991 – REVISED AUGUST 1995
QW
QX
QY
QZ
See Note A
LCLKx
td(CK-SGV)
SIGNALa
th(CK-SG)
td(SGV-SG)
td(SG-SGV)
td(SGV-SG)
tw(SGL)
tw(SGH)
td(CK-SGV)
th(CK-SG)
tt(SG)
tt(SG)
td(SG-SGV)
SIGNALb
td(SGV-SG)
td(SG-SGV)
NOTE A: Any of these quarter phases could be 2tQ if they are stretched (see clock stretch,
page 20).
Figure 35. Output Signal Characteristics
example of how to use the general output signal characteristics
Assume a system is using a SMJ34020A-32. Determine the maximum time from the start of the falling edge
of ALTCH to the time when data must be valid on LAD for a local-memory write cycle.
From the local-memory read-modify-write-cycle timing diagram on page 28, the time from the falling edge of
ALTCH to valid data on LAD is roughly Q3 + Q4; i.e., 2t_Q. A more precise value can be obtained by using the
table of output signal characteristics.
The parameter of interest is t_d(SG-SGV). Note that in Figure 35, there are two representations of t_d(SG-SGV) that
relate SIGNALa and SIGNALb (the third representation of this parameter relates SIGNALb to itself and is not
useful in this example). Let SIGNALa represent ALTCH because ALTCH is making a transition first. Let
SIGNALb represent LAD. By definition, the signal becoming valid (SGV) determines whether the fast value or
the slow value from the table is used.
In this case, for parameter t_d(SG-SGV), SGV is LAD. LAD is in the slow group, so the maximum value for t_d(SG-SGV)
is nt_Q + 22. The value for n is 2 from the analysis of the diagram on page 28. Thus, the maximum time from the
start of the falling edge of ALTCH to the time when data must be valid on LAD for a local-memory write cycle
is 2t_Q + 22 ns.
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