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SST89E54RD2-40-I-TQI Datasheet(PDF) 62 Page - Silicon Storage Technology, Inc |
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SST89E54RD2-40-I-TQI Datasheet(HTML) 62 Page - Silicon Storage Technology, Inc |
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62 / 81 page  62 Data Sheet FlashFlex51 MCU SST89E52RD2/RD / SST89E54RD2/RD / SST89E58RD2/RD SST89V52RD2/RD / SST89V54RD2/RD / SST89V58RD2/RD ©2006 Silicon Storage Technology, Inc. S71255-05-000 5/06 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 VIL and VIH specifications. 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 More specific information about on-chip oscillator design can be found in the FlashFlex51 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. FIGURE 13-1: Oscillator Characteristics TABLE 13-1:Recommended Values for C1 and C2 by Crystal Type Crystal C1 = C2 Quartz 20-30pF Ceramic 40-50pF T13-1.0 1255 TABLE 13-2: Clock Doubling Features Device Standard Mode (x1) Clock Double Mode (x2) Clocks per Machine Cycle Max. External Clock Frequency (MHz) Clocks per Machine Cycle Max. External Clock Frequency (MHz) SST89E5xRD2/RD 12 40 6 20 SST89V5xRD2/RD 12 33 6 16 T13-2.0 1255 1255 F32.0 XTAL2 XTAL1 VSS C1 Using the On-Chip Oscillator External Clock Drive C2 XTAL2 XTAL1 VSS External Oscillator Signal NC |
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