SST89V54RD2 Silicon Storage Technology, Inc., SST89V54RD2 Datasheet - Page 61

• Manufacturer Part Number: SST89V54RD2
• Description: Flashflex51 Mcu
• Manufacturer: Silicon Storage Technology, Inc.

FlashFlex MCU
SST89V54RD2/RD / SST89V58RD2/RD
13.0 SYSTEM CLOCK AND CLOCK OPTIONS
13.1 Clock Input Options and Recom-
mended Capacitor Values for Oscillator
Shown in Figure 13-1 are the input and output of an inter-
nal inverting amplifier (XTAL1, XTAL2), which can be con-
figured 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 applica-
tion to another. C1 and C2 should be adjusted appropri-
ately for each design. Table 13-1, shows the typical values
for C1 and C2 vs. crystal type for various frequencies
TABLE 13-2: Clock Doubling Features
©2007 Silicon Storage Technology, Inc.
Device
SST89V5xRD2/RD
FIGURE 13-1: Oscillator Characteristics
IL
and V
Using the On-Chip Oscillator
C 1
IH
C 2
specifications.
Machine Cycle
Clocks per
12
Standard Mode (x1)
XTAL2
XTAL1
V
SS
Max. External Clock Frequency
(MHz)
33
61
TABLE 13-1:Recommended Values for C1 and
More specific information about on-chip oscillator design
can be found in the FlashFlex Oscillator Circuit Design
Considerations application note.
13.2 Clock Doubling Option
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 refer to
Table 13-2 for detail.
Clock double mode can be enabled either via the external
host mode or the IAP mode. Please refer to Table 4-2 for
the IAP mode enabling commands (When set, the EDC#
bit in SFST register will indicate 6 clock mode.).
The clock double mode is only for doubling the inter-
nal 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.
Ceramic
Crystal
Machine Cycle
Quartz
Clocks per
Oscillator
External
Signal
External Clock Drive
C2 by Crystal Type
6
Clock Double Mode (x2)
NC
Max. External Clock Frequency
XTAL2
XTAL1
V
SS
(MHz)
C1 = C2
20-30pF
40-50pF
S71255-10-000
16
Data Sheet
1255 F32.0
T13-1.0 1255
T13-2.0 1255
12/07