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DAN-138 Datasheet(PDF) 2 Page - Exar Corporation |
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DAN-138 Datasheet(HTML) 2 Page - Exar Corporation |
2 / 8 page DATA COMMUNICATIONS APPLICATION NOTE DAN138 2 • The oscillator circuitry is similar and will operate in most cases, but there are some differences when using a crystal oscillator and when using an external clock. See Figure 1 for the differences in the oscillator circuitry for a crystal oscillator. When using an external clock input for frequencies greater than 24 MHz, Exar’s 2- channel UARTs will require a 2K pull-up resistor on the XTAL2 pin. 1.2 BUS TIMING DIFFERENCES • The TL16C752B requires that the -CS pin be asserted first before the -IOR or -IOW pin and the -IOR or -IOW pin must be de-asserted before the -CS pin is de-asserted. During a read, the Exar 2-channel UARTs can have either the -CS or the -IOR signal asserted first and have either signal be de-asserted first. The signals are wire-ORed in the Exar 2-channel UARTs, therefore the second signal asserted will initiate the read cycle and the first signal de-asserted terminates the read cycle. The same is true during a write for -CS and -IOW. The flexibility of the Exar 2-channel UARTs timing can be important in DSP, ARM, and MIPS designs. Also, because of this flexibility, the Exar 2-channel UARTs will work with the timing used for the TL16C752B. FIGURE 1. CRYSTAL OSCILLATOR CIRCUITRY DIFFERENCES C1 10-30 pF C2 40-60 pF Y1 1.8432 MHz to 24 MHz R1 1.5 K Ω R2 1 ΜΩ XTAL1 XTAL2 C1 22-47 pF C2 22-47 pF Y1 1.8432 MHz to 24 MHz R1 0-120 Ω (Optional) R2 500 ΚΩ − 1 ΜΩ XTAL1 XTAL2 XR16L2550 XR16L2551 TL16C752B |
Similar Part No. - DAN-138 |
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Similar Description - DAN-138 |
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