
System Integration Module (SIM60)
MC68360 USER’S MANUAL
If two chip selects are programmed to assert in the same ad-
dress region, only the lower chip select (or RAS line) will assert.
For example, CS1 has priority over CS4.
TCYC3–TCYC0—Cycle Length in Clocks
This field determines the length of a bus cycle (see
Table 6-14). Both internal masters and
external masters use this field for their accesses to a given memory bank. In addition, an
external MC68040 uses this field for the first access of a burst access sequence.
Although TCYC3–TCYC0 is the main parameter for determining cycle length since it se-
lects the number of wait states inserted in the cycle, the total cycle length may vary for
other reasons, such as a DRAM page hit, DRAM page miss, or whether the bus master
is internal or external to the QUICC. Besides TCYC, other bits that can affect the total cy-
cle length in certain situations are WBT40, WBTQ, DWQ, DW40, EMWS, SYNC, and
TSS40 in the GMR, and TRLXQ, PGME, and BCYC in the OR. CSNTQ and CSNT40 af-
fect the CS timing, but do not affect the total cycle length.
If the user has selected an external DSACKx or TA response for this memory bank, with
the SPS or DPS bits, then TCYC3–TCYC0 are not used.
NOTES
External cycles are always three clocks or longer.
SeeTable 6-Normal DRAM cycles are three clocks when TCYC=0 and four
clocks when TCYC=1, etc. Therefore fast termination is not pos-
sible during the initial access to DRAM. Two clock DRAM cycles
are only possible when page mode is enabled for an internal
master.
If an external DSACK response is selected with either DPS in
the GMR or SPS in the OR, TCYC should not be set to zero.
Table 6-14. Cycle Length in Clocks
Internal QUICC Master Memory Bus Cycle Length
Number of Clocks
Number of Wait States
(SRAM)
Number of Wait States
(DRAM)
TCYC =
Number
Comments
Number
Comments
Numbers
02
Fast Termina-
tion
*
Undefined
3
1
3
Normal
0
4
24
1
5
35
2
6
46
3
7
57
4
8
68
5
9
……
…
15
17
14
18
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.