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15.6.1 Explanation of AC Symbols
Each symbol consists of two pairs of letters prefixed by "T" (for time). The characters in a pair
indicate a signal and its condition, respectively. Symbols represent the time between the two sig-
nal/condition points. For example, T
(Low), and signal R (RD#) condition L (Low). Table 15-7 defines the signal and condition codes.
A
Address
B
BHE#
†
C
CLKOUT
D
Input Data
G
BUSWIDTH
L
ALE/ADV#
†
The CLKOUT pin is available only on the 8XC196MC, MD microcontrollers.
15.6.2 AC Timing Definitions
Tables 15-8 and 15-9 define the AC timing specifications that the memory system must meet and
those that the microcontroller will provide.
Table 15-8. External Memory Systems Must Meet These Specifications
Symbol
T
Address Valid to Input Data Valid
AVDV
Maximum time the memory system has to output valid data after the microcontroller outputs a
valid address.
T
RD# High to Input Data Float
RHDZ
Time after the microcontroller deasserts RD# until the memory system must float the bus. If this
timing is not met, bus contention will occur.
T
RD# Low to Input Data Valid
RLDV
Maximum time the memory system has to output valid data after th e microcontroller asserts
RD#.
†
The CLKOUT pin is available only on the 8XC196MC, MD microcontrollers.
is the time between signal L (ALE/ADV#) condition L
LLRL
Table 15-7. AC Timing Symbol Definitions
Signals
Q
Output Data
R
RD#
W
WR#, WRH#, WRL#
X
XTAL1
Y
READY
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INTERFACING WITH EXTERNAL MEMORY
Conditions
H
L
V
X
Z
Definition
High
Low
Valid
No Longer Valid
Floating
15-33
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