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COP888CS Datasheet(PDF) 18 Page - National Semiconductor (TI) |
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COP888CS Datasheet(HTML) 18 Page - National Semiconductor (TI) |
18 / 53 page Reset (Continued) Oscillator Circuits The chip can be driven by a clock input on the CKI input pin which can be between DC and 10 MHz. The CKO output clock is on pin G7 (crystal configuration). The CKI input fre- quency is divided down by 10 to produce the instruction cycle clock (1/t c). Figure 7 shows the Crystal and R/C oscillator diagrams. CRYSTAL OSCILLATOR CKI and CKO can be connected to make a closed loop crys- tal (or resonator) controlled oscillator. Table 1 shows the component values required for various standard crystal values. R/C OSCILLATOR By selecting CKI as a single pin oscillator input, a single pin R/C oscillator circuit can be connected to it. CKO is available as a general purpose input, and/or HALT restart input. Table 2 shows the variation in the oscillator frequencies as functions of the component (R and C) values. TABLE 1. Crystal Oscillator Configuration, T A = 25˚C R1 R2 C1 C2 CKI Freq Conditions (k Ω)(MΩ) (pF) (pF) (MHz) 0 1 30 30–36 10 V CC = 5V R1 R2 C1 C2 CKI Freq Conditions (k Ω)(MΩ) (pF) (pF) (MHz) 0 1 30 30–36 4 V CC = 5V 0 1 200 100–150 0.455 V CC = 2.5V TABLE 2. RC Oscillator Configuration, T A = 25˚C R C CKI Freq Instr. Cycle Conditions (k Ω) (pF) (MHz) (µs) 3.3 82 2.2 to 2.7 3.7 to 4.6 V CC = 5V 5.6 100 1.1 to 1.3 7.4 to 9.0 V CC = 5V 6.8 100 0.9 to 1.1 8.8 to 10.8 V CC = 5V Note: 3k ≤ R ≤ 200k 50 pF ≤ C ≤ 200 pF CONTROL REGISTERS CNTRL Register (Address X'00EE) T1C3 T1C2 T1C1 T1C0 MSEL IEDG SL1 SL0 Bit 7 Bit 0 The Timer1 (T1) and MICROWIRE/PLUS control register contains the following bits: T1C3 Timer T1 mode control bit T1C2 Timer T1 mode control bit T1C1 Timer T1 mode control bit T1C0 Timer T1 Start/Stop control in timer modes 1 and 2, T1 Underflow Interrupt Pending Flag in timer mode 3 MSEL Selects G5 and G4 as MICROWIRE/PLUS signals SK and SO respectively IEDG External interrupt edge polarity select (0 = Rising edge, 1 = Falling edge) SL1 & SL0 Select the MICROWIRE/PLUS clock divide by (00 = 2, 01 = 4, 1x = 8) PSW Register (Address X'00EF) HC C T1PNDA T1ENA EXPND BUSY EXEN GIE Bit 7 Bit 0 The PSW register contains the following select bits: HC Half Carry Flag C Carry Flag T1PNDA Timer T1 Interrupt Pending Flag (Autoreload RA in mode 1, T1 Underflow in Mode 2, T1A capture edge in mode 3) T1ENA Timer T1 Interrupt Enable for Timer Underflow or T1A Input capture edge EXPND External interrupt pending BUSY MICROWIRE/PLUS busy shifting flag EXEN Enable external interrupt GIE Global interrupt enable (enables interrupts) The Half-Carry flag is also affected by all the instructions that affect the Carry flag. The SC (Set Carry) and R/C (Reset Carry) instructions will respectively set or clear both the carry flags. In addition to the SC and R/C instructions, ADC, SUBC, RRC and RLC instructions affect the Carry and Half Carry flags. DS012829-7 RC > 5 x Power Supply Rise Time FIGURE 6. Recommended Reset Circuit DS012829-8 DS012829-9 FIGURE 7. Crystal and R/C Oscillator Diagrams www.national.com 18 |
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