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C8051F300 Datasheet(PDF) 100 Page - List of Unclassifed Manufacturers |
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C8051F300 Datasheet(HTML) 100 Page - List of Unclassifed Manufacturers |
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100 / 174 page  C8051F300/1/2/3/4/5 100 Rev. 2.6 12.1. Priority Crossbar Decoder The Priority Crossbar Decoder (Figure 12.3) assigns a priority to each I/O function, starting at the top with UART0. When a digital resource is selected, the least significant unassigned Port pin is assigned to that resource (excluding UART0, which is always at pins 4 and 5). If a Port pin is assigned, the Crossbar skips that pin when assigning the next selected resource. Additionally, the Crossbar will skip Port pins whose associated bits in the XBR0 register are set. The XBR0 register allows software to skip Port pins that are to be used for analog input or GPIO. Important Note on Crossbar Configuration: If a Port pin is claimed by a peripheral without use of the Crossbar, its corresponding XBR0 bit should be set. This applies to P0.0 if VREF is enabled, P0.3 and/or P0.2 if the external oscillator circuit is enabled, P0.6 if the ADC is configured to use the external conversion start signal (CNVSTR), and any selected ADC or Comparator inputs. The Crossbar skips selected pins as if they were already assigned, and moves to the next unassigned pin. Figure 12.3 shows the Crossbar Decoder priority with no Port pins skipped (XBR0 = 0x00); Figure 12.4 shows the Crossbar Decoder prior- ity with pins 6 and 2 skipped (XBR0 = 0x44). Figure 12.3. Crossbar Priority Decoder with XBR0 = 0x00 VREF x1 x2 CNVSTR 01 2345 67 00 0000 00 CEX2 CP0A SYSCLK CEX0 CEX1 SF Signals PIN I/O TX0 RX0 SDA SCL P0 CP0 Port pin potentially available to peripheral SF Signals ECI T0 T1 XBR0[0:7] Special Function Signals are not assigned by the crossbar. When these signals are enabled, the CrossBar must be manually configured to skip their corresponding port pins. Note: x1 refers to the XTAL1 signal; x2 refers to the XTAL2 signal. |
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