st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 165

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

ST10F272Z2
Note:
25.8.14
25.8.15
Note:
Figure 52. External clock drive XTAL1
When Direct Drive is selected, an external clock source can be used to drive XTAL1. The
maximum frequency of the external clock source depends on the duty cycle: when 64MHz is
used, 50% duty cycle shall be granted (low phase = high phase = 7.8 ns); when for instance
32 MHz is used, a 25% duty cycle can be accepted (minimum phase, high or low, again
equal to 7.8ns).
Memory cycle variables
The tables below use three variables which are derived from the BUSCONx registers and
represent the special characteristics of the programmed memory cycle. The following table
describes, how these variables are to be computed.
Table 78.
External memory bus timing
The following sections include the External Memory Bus timings. The given values are
computed for a maximum CPU clock of 40 MHz.
Obviously, when higher CPU clock frequency is used (up to 64 MHz), some numbers in the
timing formulas become zero or negative which, in most cases is not acceptable or not
meaningless at all. In these cases, it is necessary to relax the speed of the bus setting
properly t
All External Memory Bus Timings and SSC Timings reported in the following tables are
granted by Design Characterization and not fully tested in production.
ALE Extension
Memory Cycle Time wait states
Memory Tri-state Time
A
, t
Description
C
Memory cycle variables
and t
F
.
t1
VIH2
Symbol
t
t
t
C
A
F
t2
t3
TCL x [ALECTL]
2TCL x (15 - [MCTC])
2TCL x (1 - [MTTC])
t
VIL2
OSC
Electrical characteristics
Values
t4
165/189