p89v51rb2 NXP Semiconductors, p89v51rb2 Datasheet - Page 60

• Manufacturer Part Number: p89v51rb2
• Description: 8-bit 80c51 5 V Low Power 16/32/64 Kb Flash Microcontroller With 1 Kb Ram
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89V51RB2_RC2_RD2_4
Product data sheet
6.13.1 Clock input options and recommended capacitor values for oscillator
6.13.2 Clock doubling option
6.13 System clock and clock options
Shown in
amplifier (XTAL1, XTAL2), which can be configured for use as an on-chip oscillator.
When driving the device from an external clock source, XTAL2 should be left disconnected
and XTAL1 should be driven.
At start-up, the external oscillator may encounter a higher capacitive load at XTAL1 due to
interaction between the amplifier and its feedback capacitance. However, the capacitance
will not exceed 15 pF once the external signal meets the V
Crystal manufacturer, supply voltage, and other factors may cause circuit performance to
differ from one application to another. C1 and C2 should be adjusted appropriately for
each design.
frequencies.
Table 57.
More specific information about on-chip oscillator design can be found in the FlashFlex51
Oscillator Circuit Design Considerations application note.
By default, the device runs at 12 clocks per machine cycle (X1 mode). The device has a
clock doubling option to speed up to 6 clocks per machine cycle (please see
Clock double mode can be enabled either by an external programmer or using IAP. When
set, the EDC bit in FST register will indicate 6-clock mode.
The clock double mode is only for doubling the internal system clock and the internal flash
memory, i.e. EA = 1. To access the external memory and the peripheral devices, careful
consideration must be taken. Also note that the crystal output (XTAL2) will not be doubled.
Crystal
Quartz
Ceramic
Fig 28. Oscillator characteristics (using the on-chip oscillator)
Figure 28
Recommended values for C1 and C2 by crystal type
Table 57
and
shows the typical values for C1 and C2 vs. crystal type for various
Rev. 04 — 1 May 2007
Figure 29
C 2
C 1
are the input and output of an internal inverting
XTAL2
XTAL1
V
SS
P89V51RB2/RC2/RD2
C1 = C2
20 pF to 30 pF
40 pF to 50 pF
8-bit microcontrollers with 80C51 core
IL
002aaa545
and V
IH
specifications.
© NXP B.V. 2007. All rights reserved.
Table
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