DSP56F801 Motorola Inc, DSP56F801 Datasheet - Page 25

• Manufacturer Part Number: DSP56F801
• Description: 56F801 16-bit Hybrid Controller
• Manufacturer: Motorola Inc

3.5.3
The recommended method of connecting an external clock is given in
source is connected to XTAL and the EXTAL pin is grounded.
3.5.4
An internal relaxation oscillator can supply the reference frequency when an external frequency source or
crystal are not used. During a 56F801 boot or reset sequence, the relaxation oscillator is enabled by default,
and the PRECS bit in the PLLCR word is set to 0
relaxation oscillator can be deselected instead by setting the PRECS bit in the PLLCR to 1. When this
occurs, the PRECSS bit in the PLLSR (prescaler clock select status register) data word also sets to 1. If a
changeover between internal and external oscillators is required at startup, internal device circuits
Freescale Semiconductor
Frequency of operation (external clock driver)
Clock Pulse Width
1. See
2. May not exceed 60MHz for the DSP56F801FA60 device.
3. The high or low pulse width must be no smaller than 6.25ns or the chip will not function.
4. Parameters listed are guaranteed by design.
External
Note: The midpoint is V
Clock
External Clock Source
Use of On-Chip Relaxation Oscillator
Figure 3-9
Operating Conditions:
Table 3-8 External Clock Operation Timing Requirements
Characteristic
3, 4
for details on using the recommended connection of an external clock driver.
10%
50%
90%
Figure 3-9 Connecting an External Clock Signal
t
PW
IL
+ (V
Figure 3-10 External Clock Timing
IH
– V
IL
V
56F801 Technical Data, Rev. 16
)/2.
SS
External Clock
= V
t
1
PW
SSA
XTAL
= 0 V, V
56F801
Symbol
(Section
f
t
osc
PW
EXTAL
DD
V
= V
SS
3.5). If an external oscillator is connected, the
DDA
6.25
Min
0
= 3.0–3.6 V, T
Typ
Figure
—
—
A
= –40° to +85°C
3-9. The external clock
Max
80
—
3
2
External Clock Operation
10%
50%
90%
MHz
V
V
Unit
ns
IH
IL
25