W78C438C
- 12 -
AC CHARACTERISTICS
AC specifications are a function of the particular process used to manufacture the product, the ratings
of the I/O buffers, the capacitive load, and the internal routing capacitance. Most of the specifications
can be expressed in terms of multiple input clock periods (T
CP
), and actual parts will usually
experience less than a
±
20 nS variation.
Clock Input Waveform
PARAMETER
SYMBOL
MIN.
TYP.
MAX.
UNIT
NOTES
Operating Speed
F
OP
0
-
40
MHz
1
Clock Period
T
CP
25
-
-
nS
2
Clock High
T
CH
10
-
-
nS
3
Clock Low
T
CL
10
-
-
nS
3
Notes:
1. The clock may be stopped indefinitely in either state.
2. The T
CP
specification is used as a reference in other specifications.
3. There are no duty cycle requirements on the XTAL1 input.
Program Fetch Cycle
PARAMETER
SYMBOL
MIN.
TYP.
MAX.
UNIT
Address Valid to PSEN Low
T
APL
2 T
CP
-
-
nS
PSEN Low to Data Valid
T
PDV
-
-
2 T
CP
nS
Data Memory Read/Write Cycle
PARAMETER
SYMBOL
MIN.
TYP.
MAX.
UNIT
Address Valid to RD Low
T
ARL
4 T
CP
-
4 T
CP
+
∆
nS
RD Low to Data Valid
T
RDV
-
-
4 T
CP
nS
Data Hold After RD High
T
RDQ
0
-
2 T
CP
nS
RD Pulse Width
T
RS
6 T
CP
-
∆
6 T
CP
-
nS
Address Valid to WR Low
T
AWL
4 T
CP
-
4 T
CP
+
∆
nS
Data Valid to WR Low
T
DWL
1 T
CP
-
-
nS
Data Hold After WR High
T
WDQ
1 T
CP
-
-
nS
WR Pulse Width
T
WS
6 T
CP
-
∆
6 T
CP
-
nS
Note: "
∆
" (due to buffer driving delay and wire loading) is 20 nS.
