C8051F502-IM 参数 Datasheet PDF下载

C8051F50x-F51x

20.2.3. Assigning Port I/O Pins to External Digital Event Capture Functions

External digital event capture functions can be used to trigger an interrupt or wake the device from a low

power mode when a transition occurs on a digital I/O pin. The digital event capture functions do not require

dedicated pins and will function on both GPIO pins (PnSKIP = 1) and pins in use by the Crossbar (PnSKIP

= 0). External digital event capture functions cannot be used on pins configured for analog I/O. Table 20.3

shows all available external digital event capture functions.

Table 20.3. Port I/O Assignment for External Digital Event Capture Functions

Digital Function

Potentially Assignable Port Pins

SFR(s) used for

Assignment

External Interrupt 0

External Interrupt 1

Port Match

P1.0–P1.7

P1.0–P1.7

P0.0–P3.7*

IT01CF

IT01CF

P0MASK, P0MAT

P1MASK, P1MAT

P2MASK, P2MAT

P3MASK, P3MAT

*Note:

P3.1–P3.7 are only available on the 48-pin packages.

20.3. Priority Crossbar Decoder

The Priority Crossbar Decoder (Figure 20.3) 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 assigned to pins P0.4 and P0.5, and excluding CAN0 which is

always assigned to pins P0.6 and P0.7. If a Port pin is assigned, the Crossbar skips that pin when assign-

ing the next selected resource. Additionally, the Crossbar will skip Port pins whose associated bits in the

PnSKIP registers are set. The PnSKIP registers allow software to skip Port pins that are to be used for

analog input, dedicated functions, or GPIO.

Because of the nature of Priority Crossbar Decoder, not all peripherals can be located on all port pins.

Important Note on Crossbar Configuration:

If a Port pin is claimed by a peripheral without use of the

Crossbar, its corresponding PnSKIP bit should be set. This applies to P0.0 if VREF is used, P0.1 if the

ADC is configured to use the external conversion start signal (CNVSTR), P0.3 and/or P0.2 if the external

oscillator circuit is enabled, 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.

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Rev. 1.1