SMJ34020A Datasheet, PDF (22/92 Pages) Texas Instruments – GRAPHICS SYSTEM PROCESSOR

SMJ34020A
GRAPHICS SYSTEM PROCESSOR
SGUS011B – APRIL 1991 – REVISED AUGUST 1995
enabling clock stretch (continued)
The following are examples of stretch-mode memory operations.
two 32-bit nonpage-mode reads
ADDR
READ
ADDR
READ
1234123412341234
Stretch Mode Disabled
ADDR
READ
ADDR
READ
Stretch Mode Enabled
123441234123441234
Stretch
Stretch
one 32-bit page-mode read-modify-write
ADDR
READ
WRITE
123412341234
Stretch Mode Disabled
ADDR
READ
WRITE
Stretch Mode Enabled
12344123441234
Stretch
Stretch
three 32-bit page-mode reads
ADDR
READ
READ
READ
1234123412341234
Stretch Mode Disabled
ADDR
READ
READ
READ
Stretch Mode Enabled
12344123412341234
Stretch
The stretched cycles are designed to accommodate worst-case 32-bit page-mode accesses, so during some
nonpage-mode memory accesses stretches that are not essential can be generated. For example:
one 32-bit nonpage-mode read-write
ADDR
READ
ADDR
WRITE
1234123412341234
Stretch Mode Disabled
ADDR
READ
ADDR
WRITE
Stretch Mode Enabled
1234412344123441234
Stretch
Stretch
Stretch
Stretches are inserted in read-modify-write accesses to help ease bus turn-around timings. In the above
example, the second stretch is not needed to help these timings because the read/write turn-around has the
whole of the address cycle to evaluate.
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